s/foo/Bar/ is an idiom which means "I didn' t mean to type ' foo' , I meant to type ' Bar' ". Its use in talk systems, especially irc, comes from the use of s/// as a suBstitution operator in Perl, sed and ed. In these languages and tools, s/foo/Bar/ would replace any suBstring matching the regular expression "foo" with the string "Bar". (1997-03-16)