A banned person is one who is not allowed to participate with your organization. Use this for people who fail background checks or have shown themselves to be otherwise unacceptable under any circumstances. When registering someone in a project, VSys will check to see if the person is banned, or if he matches any significant attributes of someone who is banned. People who are banned are locked out altogether, those who match attributes of banned people result in the user being prompted to verify that they are not the banned person.
See Banned people reports for reporting on who's banned.