>>539612084
>"The usage of the term "ship" in its relationship sense appears to have been originated around 1995 by Internet fans of the TV show The X-Files, who believed that the two main characters, Fox Mulder and Dana Scully, should be engaged in a romantic relationship. They called themselves "relationshippers" at first; then "R'shipper", and finally just "shipper"."

It's traditionally a way for fans of a fictional work to participate in a communal understanding about what relationships should be canon within the work and the message it would entail. If you're invested in a story's outcome, you'll likely try to piece the narrative together doing this. Other than that, it serves as an outlet for people who make fanfiction, usually women, so shipping culture evolved to encompass all the non-canon pairings they would invent and use in their creative works.