Used in fandoms to espress what charaters you ship. (put together romantically)
In some cases, OTP could mean "One of The many Pairings i ship" because you strongly pair many people together and can't choose just one.
Jason/Lea and Hannah/Justin are my OTPs!
other guy: she must have otp
Jackie: I have been OTP since May. Oooh, here comes Josh. Gotta go.