A kibitzer is a non-participant who hangs around a game, offering (often unwanted) advice or commentary. This Yiddish term is used in Contract bridge

Contract bridge

Contract bridge, usually known simply as bridge, is a trick-taking card game using a standard deck of 52 playing cards played by four players in two competing partnerships with partners sitting opposite each other around a small table...

, Chess

Chess

Chess is a two-player board game played on a chessboard, a square-checkered board with 64 squares arranged in an eight-by-eight grid. It is one of the world's most popular games, played by millions of people worldwide at home, in clubs, online, by correspondence, and in tournaments.Each player...

, Go, and many other games.

Kibitz is also a term referring to circular commenting. One person comments, then the other person comments. A back-and-forth conversation outside the main issue, where the people having the conversation are not directly participating.

This term has found a home in computer science. NIST released a sub-project of the Expect

Expect

Expect is a Unix automation and testing tool, written by Don Libes as an extension to the Tcl scripting language, for interactive applications such as telnet, ftp, passwd, fsck, rlogin, tip, ssh, and others. It uses Unix pseudo terminals to wrap up subprocesses transparently, allowing the...

 programming language called kibitz that allows two users to share one shell session, taking turns typing one after another.

There is a 1930 film called The Kibitzer which is based on the 1929 three-act comedy play by the same name.

Jane Jacobs refers to a kibitzer as someone who can look out onto a street, and if they saw any suspicious activity, will intervene and help the victim. In this way, kibitzers help keep streets safe.

Kibitzer is both Schwabian (South German) and Yiddish and means 'nosy person' (neugierig).