A Usermap allows GameFAQs to track all accounts that a person holds. GameFAQs allows users to have more than one account and many users gratefully use this option to maintain one or more alt accounts. However, there is potential for abuse here - people could use an alternate account to flame or troll other users while keeping their identity secret and their main account safe from moderation.
To at least combat the latter, GameFAQs tracks users across all their accounts. Accounts that appear to belong to the same user (because they're used from the same computer/connection) or that are shared between multiple users are tracked on a usermap, allowing moderators and administrators to see which accounts are associated with which user.
If a user posts violations severe or numerous enough to warrant a ban, the administrator can at his discretion apply further punishments (usually purgatory or other bans) to other accounts on the usermap. If a usermap's entire contents are banned this is popularly referred to as a usermap axe.
While a usermap normally contains only the accounts belonging to a single user, there are cases where multiple people using the same computer (siblings, for instance) or users having one or more shared accounts between them result in a user being punished for the acts of somebody else. This is unavoidable, however, as in such cases it is not possible for GameFAQs to tell the difference between the people in question. Because of this, GameFAQs users are advised not to share accounts; and to keep an eye on unruly little brothers.