In internet|lang=en terms the difference between invisible and ghost
is that invisible
is (internet) apparently, but not actually, offline while ghost
is (internet) an unresponsive user on irc, resulting from the user's client disconnecting without notifying the server.
As an adjective invisible
is unable to be seen; out of sight; not visible.
As a noun ghost is
(rare) the spirit; the soul of man.
As a verb ghost is
(obsolete|transitive) to haunt; to appear to in the form of an apparition.