A term used on fan sites, a shipper is a fan fiction writer or fan of a TV show, movie, etc. that writes or views the principals (the main or secondary characters) as having a romantic and/or sexual relationship that is not within the
boundaries set by the particular movie or TV show. Fan fictions written by
shippers contain varying degrees of sexual content and varying degrees of
slash content (M/F, F/F, M/M, see below).
Known primarily as an "X-Files term" (from the popular TV series) it refers to people who believe there is a romantic relationship between Scully and Mulder. You see this term a lot in chat rooms as there are many X-Files Web sites (known as "XF") even though the show has been cancelled and only reruns are on the air.
This term is also appropriated by other fandoms. For example, a shipper is a viewer of a sci-fi or fantasy TV
show (such as Star Trek, Babylon 5) who writes erotic fiction about
fantasized relationships between the show's stars. It is similar to the older
fan-fiction term "slash" for the imagined homoerotic pairings (as in Kirk/Spock).