A ghost session occurs when an IRC user gets disconnected and the server doesn't know about it (for example, when the user's computer or modem crashes). Ghosts occur due to the implementation of the IRC protocol, where particularly abrupt disconnections may not be noticed by the server for several minutes. NickServ implementations generally include a "GHOST" command which will disconnect a ghost (or nefarious user) that is using your nickname. Syntax:
/ghost nickname password /ns ghost nickname password
