OTP
An abbreviation for one true pairing: a fan’s favorite or ideal romantic couple.
“They are my OTP; no other pairing in the series comes close.”
Fans use OTP for the pairing they feel most strongly about, whether the couple is official, implied, or entirely imagined.
One true pairing emerged in online fanfiction and fandom communities in the late 1990s and early 2000s.
one true pairing
The phrase written out in full.
OT3
A favorite romantic grouping of three people.
NOTP
A pairing someone strongly dislikes.
Can someone have more than one OTP?
Despite the word one, many fans use OTP loosely for several favorite pairings.
Does OTP also mean one-time password?
Yes. In security contexts, OTP usually means one-time password.