Oranges, Tangerines, Persimmons

Depends on context! For example, in a fandom (fans of a particular franchise/ television show/ book/ movie/ game) OTP is the abbreviation of One True Pairing, or the "ship" that is your most important. This means that you are invested in romantic development between two characters, and hold it above any other potential romantic developments. Another interpretation of the abbreviation includes "over the phone", meaning to discuss while using the telephone.

One Time Password

Over the phone

It can also mean One Trick Pony ( someone only knows/ does one thing but that usually very well )