A check to the minor edit box is intended to signify that only superficial differences exist between the current and previous version: typo fixes, formatting, or otherwise rearranging text without changing content. A minor edit is a version that the editor believes requires no review and could never be the subject of a dispute.
By contrast, a major edit is a version that should be reviewed by other editors to ensure that everyone agrees on the change. Therefore, any change that affects the meaning of an article is not minor, even if the edit is a single word.
The distinction between major and minor edits is significant because editors may choose to ignore minor edits when reviewing recent changes; logged-in users might even set their preferences to not display them. If you think there is any chance that another editor might dispute your change, please do not mark it as minor.
An edit marked as minor is signified with a bolded "m" character (m) in the page history. Minor edits will also appear with the same bolded "m" in Special:RecentChanges.
Simple formatting or grammar correction (capitalisation, et cetera)
Formatting that doesn't change the meaning of the page (e.g. bolding text, splitting one paragraph into two)
Obvious factual errors (changing The Beatles' 1866 album to The Beatles' 1966 album)
Fixing layout errors
Adding and correcting wiki links or categories
Removing vandalism and graffiti
Things to remember
Any change to the source text (Wikitext), even if it does not affect the presentation of the page in HTML (if it involves adding a space or a line break, for example) will still be treated as a change according to the database.
Marking a major change as a minor one is considered poor etiquette, especially if the change involves the deletion of some text.
Reverting a page is not likely to be considered minor under most circumstances. When the status of a page is disputed, and particularly if an edit war is brewing, then it is better not to mark any edit as minor. Reverting blatant vandalism is an exception to this rule.
Who can mark an edit as minor?
Users who are not logged into Wikia are not permitted to mark changes as minor because of the potential for vandalism. The ability to mark changes as minor is another reason to register.
An administrator, or a user with rollback rights (see Help:User access levels) can semi-automatically revert the edits of the last editor of a page; all such "rollback" reversions are marked as minor by the wiki software. This is because the cumulative effect of the edits and the rollback is nothing.
The intended use of the rollback feature is for cases of vandalism, where the act of reverting any vandalism should be considered minor (and can be ignored in the recent changes list). This has the undesirable effect that if preferences have been set to hide minor edits, and an undesirable edit has not been marked minor, one sees that, but not a possible semi-automatic reversion, in Recent Changes and Enhanced Recent Changes.