OTR
OTR or Otr may refer to:

Science and technology
 Off-the-Record Messaging, an instant messaging encryption protocol
 Oxygen transmission rate, of a substance
 Otaara, a plant genus

Entertainment
 Old-time radio, a broadcasting era
 Off the Record with Michael Landsberg, a sports talk show

Music
 On the Rocks (band)
 Otierre, an Italian hip hop band

Other uses
 Coto 47 Airport, in Costa Rica
 Occupational Therapist, Registered, Licensed
 On the Run (convenience store)#Australia
 Ótr, a mythical dwarf
 Over-the-Rhine, a neighborhood in Cincinnati, Ohio, US
 Over the road, truck drivers without schedule or route