A combination of the names "Mulder" and "Scully" of The X-Files fame. It is a term not used in most of the X-Files fandom. As an older fandom that grew right at the beginning of the Internet revolution the combination of names was not as common as other fandoms. I.E. Harry Potter. Use of 'Sculder' on older lists and message boards will get the user laughed at and mocked.
The proper term is shipper
as the term originated in the X-Files fandom