Hello. Could we have a little explanation about account suspension please? What is it?

I've been noticing the ''account suspended" on two new members with less than 100 posts, it's just worrying me because I don't know what I don't know, they seemed like decent folks. Is it always an administrative decision? Can a member ask for it for some reasons?

What I really like to know is that, what are the chances that they'll come back and post on the same account? I hope you get my meanings of my questions on this post.