From The Jargon File (version 4.4.7, 29 Dec 2003) :
sysop
/sis'op/, n.
[esp. in the BBS world] The operator (and usually the owner) of a
bulletin-board system. A common neophyte mistake on FidoNet is to address
a message to sysop in an international FidoNet board, thus sending it to
hundreds of sysops around the world.