Blocked users are users who are unable to edit pages, upload files, move pages, and perform other actions that additional user rights would grant. Sysops or others with access to the blocking and unblocking interface may not block nor unblock others (except themselves) while blocked.
Blocked users can still view and edit their watchlists; and on most (but not all) wikis, can still edit their own user talk page and/or send e-mails using Special:EmailUser (registered accounts only) unless specifically disallowed. Administrators, Bureaucrats (on most wikis), and Stewards can block users (unregistered or logged in). Global sysops can also block users on wikis opted in to the global sysop wikiset.