OTR

OTR may refer to:

Old-time radio, a term describing an era of radio programmes in the first half of the 20th century.
Off-the-record messaging, an instant messenger encryption technology.
Oxygen Transmission Rate, a measure of a barrier material's oxygen permiability.
Off-Topic Republic, a sect of the Toolkitzone.com
Organisation and Technology Research (OTR plc), a European IT research company
Off the Record (TV series), A Canadian sports talk show.
Over the Rhine, a Cincinnati-based band