- (cryptography) one-time pad
- (fandom slang) One true pair (or pairing), the romantic pairing preferred by an author or reader of fan fiction.
- (electronics) one-time programmable, for electronic devices that can only be programmed once.
- (instant messaging) On the phone.
- (computing) one time password, a password that is valid for only one login session or transaction.
- (telecommunications) wikipedia:Open Telecom Platform.
- (computing) wikipedia:Opposite Track Path.