Some users have been banned. They and some other editors have been blocked. Banned editors are usually established editors who have been determined to so disruptive to Wikipedia that they should not be permitted onto the site. Extremely disruptive editors have sometimes been banned "indefinitely". They are listed at Wikipedia:List of banned users
Banned users are "blocked". Blocked editors are unable to edit the wiki, but may still view the site. Often blocks are brief, as short as a few minutes, but are more often for a day or two due to minor infractions such as edit warring. There is a list of active blocks at the special page: Blocked IP addresses and usernames
Other users have been blocked indefinitely as vandals. Those accounts never became established editors. They just came on and engaged in vandalism over and over, created other accounts which engaged in vandalism over and over, etc. Some of these never created an account, just edited anonymously, sometimes through rotating addresses.
Blocking or banning anyone is a failure of one of the premises Wikipedia is built on: people can work together constructively to create a common resource for the use of humanity. An attempt is made to permit everyone to participate.