Name sniping is the act of registering a new account for the purpose of taking a special username (typically a word in the dictionary or a legible phrase, or small usernames). Users who partake in this act are known as name snipers, and occasionally make "list accounts" with the special name (such as "ExploiterList") and use the description to name different users of that type. This is synonymous with tracker accounts, where the account lists every account that meets the criteria, such as an administrator.
Name sniping can be used maliciously, such as through impersonation. This occurs when a player creates a similar username to another notable player and pretends to be that account. For instance, Builderman could have been name-sniped as BuiIderman (capital i instead of lowercase L). This can become malicious, particularly if that account is used to scam players who are unable to identify the difference. Of course, that isn't the usual intent of name sniping.