One True Pairing - Fanlore

You may be looking for the zine publisher OTP Press (aka One True Pairing Press) or the zine publisher OTP Press (aka Other Times and Places Press).

"One True Pairing" is abbreviated as OTP -- it is the sole or primary pairing someone is interested in for a given fandom. Someone with an OTP may have little or no interest in reading or creating fanworks for other pairings, although they may still be interested in reading/producing gen. Fans who do read or create fanworks for multiple pairings in a single fandom may or may not have an OTP; if they do, they may describe their favorite pairing as their OTP.

Contemporary Usage

The term and its derivatives are largely synonymous with shipping, e.g. "I ship Harry/Hermione" can mean "My OTP is Harry/Hermione". However, while one may ship more than one pairing in any given fandom, OTP is used to single out a fan's favorite pairing in that fandom.

Original Usage

Actually, according to the original use of the term, back in the days of Mono-Fandom fans, the term OTP meant the only pairing that the fan was interested in, period. There wasn't even a second fandom, let alone a second pairing within the fandom, that was included as part of the definition.

OT3

OT3 is a play on OTP, and means "one true threesome". Its use is generally looser than OTP; OT3 tends to mean "the threesome I really like" more than "I'm only interested in this threesome and no other pairings or combinations." In some contexts, "trio" is a synonym for OT3.

OT4

OT4 means "one true foursome", and is a riff off OTP and OT3. When used on a story it generally means an actual sexual foursome, but it's also sometimes used by readers to describe a warm gen "team" story that made them feel like the four people are (or could be) "together" -- a sort of team smarm. It is fairly popular in SGA and Merlin, although marginal compared to the common OTPs John/Rodney and Arthur/Merlin; for details on SGA, see Stargate Atlantis/OT4; for Merlin, see Merlin (BBC)/OT4/5.

OT5

"One true fivesome," is used in Merlin (BBC) fandom to refer to stories in which Merlin, Arthur, Guinevere, Morgana, and Lancelot are all involved in a single relationship or pattern of intertwining relationships.

It's also used in Prince of Tennis fandom, generally to refer to Fuji/Tezuka/Echizen/Atobe/Sanada stories. OT6 occasionally shows up too, adding Yukimura to the group. However it sometimes refers to a slightly different group of five or six characters, PoT having a large surplus of attractive boys.

The term also appears frequently in Arashi fandom.