To revert is to undo all changes made to an article page after a specific time in the past. The result will be that the page becomes identical in content to the page saved at that time. However in the context of the three revert rule, a revert is defined far more broadly as any change to an article that partially or completely goes back to any older version of an article.
A partial revert is accomplished either by an ordinary edit of the current version, or by editing an old version. The former is convenient, for example, for a partial reversion of a recent addition, while the latter is convenient for a partial reversion of a deletion.
Below is some Wikipedia-oriented text on reversion.
When to revert 
- Reverting is a decision which should be taken seriously.
- Reverting is often used for fighting vandalism, or anything very similar to the effects of vandalism.
- If you are not sure whether a revert is appropriate, discuss it first rather than immediately reverting or deleting.
- If you feel the edit is unsatisfactory, improve it if possible. Improving may entail factual or grammatical corrections, or style changes such as trimming verbosity. If the material is too nonsensical, trivial, or poorly written to be improved, you may need to revert it completely.
- You can revert your own edit if you realize that it is wrong (you should have noticed this in the preview, though). Be careful if some other editor has made changes in the interim.
- Do not simply revert changes that are made as part of a dispute. A revert on the basis of a factual dispute is inappropriate unless, and only unless, you as an editor possess firm, substantive, and objective proof to the contrary. Mere disagreement is not such proof. Be respectful to other editors, their contributions and their points of view. Assume good faith.
- Try to consider the editor "on the other end" but remember that our duty is to the reader. Though your intentions may be good, don't let superfluous or badly-written material stand in order to avoid slighting its original author. Doing so shirks your duty to the reader.
- If your material is reverted, don't take it personally. Not every fact, detail, and nuance belongs in an encyclopedia.
- If the edit you are considering reverting can instead be improved (for example, to avoid weasel words, or to re-phrase in a more NPOV way), then reword, don't revert.
- Generally there are misconceptions that problematic sections of an article or recent changes are the reasons for reverting or deletion. If they contain valid and encyclopedic information, these texts should simply be edited and improved accordingly.
- There's sometimes trouble determining whether some claim is true or useful, particularly when there are few people "on board" who are knowledgeable about the topic. In such a case, it's a good idea to raise objections on a talk page; if one has some reason to believe that the author of what appears to be biased material will not be induced to change it, editors have sometimes taken the step of transferring the text in question to the talk page itself, thus not deleting it entirely. This action should be taken more or less as a last resort, never as a way of punishing people who have written something biased. See also Wikipedia:Neutral point of view/FAQ
- If there is or has been a recent poll or similar discussion about the change, do not revert a change made in lack of consensus just because "there is no consensus in favour of the change". Only revert if you actually think the previous version is so much better that you would have supported a proposal for a change in the opposite direction.
How to revert 
- Go to the page, click on "history" at the top ("Page history" in some skins), and click on the time and date of the earlier version to which you wish to revert.
- Then when that page comes up, you'll see something like "(Revision as of 22:19 Aug 15, 2002)" below the title and beneath "From Wikipedia, the free encyclopedia".
- Verify that you've selected the correct version, and click to edit the page, as you would normally. Important: in the case of vandalism, take the time to make sure that you are reverting to the last version without the vandalism; there may be multiple consecutive vandal edits, sometimes interspersed with constructive edits.
- You'll get a warning, above the edit box, about editing an out-of-date revision.
- After heeding the warning, save the page. Be sure to add the word "revert" and a brief explanation for the revert to the edit summary. Some Wikipedians abbreviate "revert" as "rv". A useful addition is to Wikilink the usernames associated with the versions you are reverting from and to. For example, a good edit summary when reverting vandalism would be
rv edits by 127.0.0.1 to last version by ExampleThe clickable links are created by entering [[User:Username|]] (replacing Username with the real IP address or Username, for logged-in users). Thus for an edit summary that reverts vandalism you would type exactly: rvv edits by [[User:127.0.0.1|127.0.0.1]] to last version by [[User:Example|Example]]
- Click on "history" again. A new line will have been added, and you'll be able to verify (by clicking on "last") that you undid the vandalism plus all subsequent bona fide edits, if any. You are responsible for redoing all the subsequent edits which you undid.
- Hint: In a vandalism case where sections of text were simply deleted and then subsequent edits were made by others, it may be easier for you to cut and paste those missing sections of text back in, than to revert and then re-do the edits.
- Check the contribution history of the user who vandalized the article. (Click on their IP address or username. That will often bring you directly to their User contribution page, if you clicked on their IP address. If you are able to click on their username, that will bring you to their User page. In the lower left-hand corner, there is a toolbox with a "User contributions" link. Click that.) If this user is vandalizing many articles, please report them to Wikipedia:Vandalism in progress.
Reverts do not cause edit conflicts 
Reverts never cause an edit conflict - if between the moment you begin the revert process, and the moment you click Post (or Save page), someone else edits and saves the page, their edits will be silently overwritten by the reverted version (but still appear in the page history). So beware of reverting high-traffic pages! Conversely, if it looks like someone has deleted your edits, consider whether it may be one of these unfortunate revision conflicts.
Instead of removing all changes after a certain version, the latest versions of MediaWiki allow a single edit to be undone. To do this, view the diff for the edit, and click on 'undo' above the newer version. The software will attempt to create an edit page with a version of the article in which the undone edit doesn't exist but all later edits are retained. There is a default edit summary, but it can be changed.
This feature removes the need to manually redo useful changes since the "undone" edit. However, it will fail if undoing the edit would conflict with later edits. For example, if edit 1000 adds a paragraph and edit 1005 modifies that paragraph, it will be impossible to automatically undo edit 1000. In this case, you must determine how to resolve the problem manually.
Admin features 
On the user contributions page, admins have the additional "rollback" links at lines which are the last edit made by anybody to that article. Some user scripts (mentioned below) also give users the ability to rollback with an automated edit summary. The rollback link is also shown on the diff page when viewing the difference between any version of the page and the most recent one. Clicking on the link reverts to the previous edit not authored by the last editor, with an automatic edit summary of "Reverted edits by X (talk) to last version by Y," which marks the edit as "minor." If, between loading the User Contributions page and pressing "rollback," someone else edits or rolls back the page, or if there was no previous editor, you will get an error message.
The rollback link on the diff page is somewhat misleading, because reversion is not necessarily to the old version shown (the diff page may show the combined result of edits including some by other editors, or only part of the edits the rollback button would revert). To see the changes the rollback button would revert, view the corresponding diff page.
Rollbacks should be used with restraint, in part because they leave no explanation for the revert in the edit summary. Rolling back a good-faith edit without explanation may be misinterpreted as "I think your edit was no better than vandalism and reverting it doesn't need an explanation." Some editors are sensitive to such perceived slights; if you use the rollback feature other than for vandalism, it's polite to leave an explanation on the article talk page or on the talk page of the user whose edit(s) you reverted.
- Sam Hocevar's godmode-light.js script adds functionality similar to the admin rollback links described below. More info at WP:US.
- The vandal edit can also be reverted using popups or monobook-suite.
Bot rollback 
In cases of flood vandalism, admins may choose to hide vandalism from recent changes. To do this, add &bot=1 to the end of the URL used to access a user's contributions. For example, http://en.wikipedia.org/w/wiki.phtml?title=Special:Contributions&target=SomePersistentVandal&bot=1.
When the rollback links on the contributions list are clicked, the revert, and the original edit that you are reverting will both be hidden from recent changes unless you click the "bots" link to set hidebots=0. The edits are not hidden from contributions lists, page histories or watchlists. The edits remain in the database and are not removed, but they no longer flood Recentchanges. The aim of this feature is to reduce the annoyance factor of a flood vandal with relatively little effort. This should not be used for reverting a change you just don't like, but is meant only for massive floods of simple vandalism.
Revert wars considered harmful 
Revert wars are usually considered harmful for the following reasons:
- They cause ill-will between users and negatively destabilize articles.
- They make the page history less useful, waste space in the database.
- Some editors are sensitive, and to them a revert is a bit like a slap in the face: "I worked hard on those edits, and someone just rolled it all back."
- They make it hard for other people to contribute, and flood recent changes and watchlists.
Editors should not revert simply because there is disagreement. Instead explore alternate methods like raising objections on a talk page, or following the processes in dispute resolution.
Three revert rule 
- Main article: Wikipedia:Three revert rule
As a means to limit edit wars, Wikipedia policy states that you may not revert any article more than three times in the same day. This is a hard limit, not a given right. Attempts to circumvent the three-revert rule (such as making a fourth revert just after 24 hours) are strongly discouraged, and may trigger the need for remedies such as your being blocked from editing.
Explain reverts 
When a revert is necessary, let people know why you reverted. The person whose material you reverted may then be able remake their edit, but fixing whatever problem it is that you've identified.
Explaining reverts also helps other people. For example, it lets people know whether they need to even view the reverted version (in the case of, e.g., "rv page blanking"). Because of the lack of non-verbal communication online, if you don't explain things clearly people may assume the wrong thing, and that's one of the possible causes for edit wars. Explaining reverts also helps people who are using the encyclopedia article and checking the edit history to see to what extent they can rely on the information in the article.
If your reasons for reverting are too complex to explain in the edit summary, drop a note on the Talk page. A nice thing to do is to drop the note on the Talk page first, and then revert, rather than the other way round. Sometimes the other person will agree with you and revert for you before you have a chance. Conversely, if someone reverts your change without apparent explanation, you may wish to wait a few minutes to see if they explain their actions on the article's talk page or your user talk page.
Edits that don't contribute to edit warring are generally considered to be exceptions to the 3-revert rule. Such edits may include reverts of obvious vandalism, reverts of banned users, or removal of potentially libelous text. See Wikipedia:Three-revert rule#Exceptions for a fuller explanation.
Please request protection rather than reverting. Violation of this rule may lead to protection of the page on the version preferred by the non-violating party; blocking; or investigation by the Arbitration Committee.