[for a thing to be] available to the public again. (Said especially
of things that are said to circulate, such as money, library books, and magazines.) (Formal)
[for a person to be] socially active again; dating again after a divorce or breakup with one's lover. (Informal).
I've heard that gold coins are back in circulation in Europe.
I would like to read War and Peace. Is it back in circulation, or is it still checked out?
Now that Bill is a free man, he's back in circulation.
Tom was in the hospital for a month, but now he's back in circulation.