In fandom, one who supports a certain relationship between two characters or believes it will come about. Originally came about as the word ship, short for relationship.
For example, there are many Mulder/Scully shippers in the X-Files fandom, and a veritable war going in the Harry Potter fandom between the Harry/Hermione shippers and the Ron/Hermione shippers.
Can also be a verb, as in "Why do you think I'm crazy just because I ship Frodo/Gollum?"