When people talk about fandom, one of the first things that pop into their heads is about fanfiction, and fanart. While some of these works are more general adventure stories a large amount of fan work is based on a ship or a romantic pairing of characters. (Ship is shortened from relationship).
Shipping first reached documented 'mainstream' with Kirk and Spock in the 1960s though the term shipping was first used by fans of the X-files wanting Mulder and Scully to finally get together. The advent and rise of the internet spread shipping as now fans were able to better find others to talk about their pairings, and a better space to share their works with wider audiences.
Many ships come up with their own name, usually a portmanteau of the two characters name, such as Drarry (Draco and Harry from Harry Potter), Korrasami (Korra and Asami from Legend of Korra), and Sherlolly (Sherlock and Molly from the BBC's Sherlock). This also happens with celebrity couples in Hollywood gossip magazines like Bennifer (Jennifer Lopez and Ben Affleck) and Kimye (Kim Kardashian and Kanye West) are just a few examples.
However, some ship names aren't quite so obvious like frostiron (Loki and Tony Stark from the Marvel Cinematic Universe) where it's the combination of Iron Man and Loki being a frost giant; JavaJunkie (Luke and Lorelai from Gilmore Girls) which is based on their mutual coffee obsessions and coffee shop meet ups. These names come from idiosyncrasies within the shows that fans know. This naming can make many ship names appear to be nonsensical to non-fans. These names help fans organize, tag, and find new work. Many of these tags become their own community of fans who share fanworks, thoughts, and personal information.
Many pairings use multiple names and there can be discord within the community of shippers about which name is the correct name. To avoid confusion, some also label fanwork "Character A X Character B" to let others know exactly who the pairing is without relaying on a ship name.
The terms, OTP, BrOTP, OT3, and OT4 (and probably onwards to infinity) come up frequently in ships. OTP is a 'One True Pairing' while a BrOTP is a portmanteau of 'Bromance' (a friendship between two people) and OTP to mean a best friendship while OT3 and OT4 are for three or four characters involved with one another.
So why do people ship?
The reasons range widely from person to person. For some, it's a safe way to explore relationships and sexuality, for others it's wish fulfillment, for others it's a way to bring lgbtqia representation to their media. For some it's a social activity and a way to complete creative works and have a built in audience.
Regardless of the whys behind shipping, it's clear that relationships are here to stay as an important and vibrant part of the fandom community.