Old Stone Age (Paleolithic)

OSA as an acronym can stand for:

Office of Secret Actions, a fictional government department in Return to Castle Wolfenstein

Open Scripting Architecture for AppleScript

Optical Society of America

Official Secrets Act

9K33 Osa (SA-8 Gecko), a Soviet surface-to-air missile launcher

Ontario Soccer Association

Osa class missile boat

Operation Save America

The old airport code for Osaka International Airport

OSA Group, a Constructivist architectural association of the 1920s based in the USSR

Osa (plant), a genus of plants in the Rubiaceae family

In signal processing, oversampling is the process of sampling a signal with a sampling frequency significantly higher than twice the bandwidth or highest frequency of the signal being sampled. An oversampled signal is said to be oversampled by a factor...

Oscilloquartz SA

Old Scona Academic High School, a school in Edmonton, Canada

Osa, name of several rural localities in Russia

Open Solutions Alliance

Online Savings Account

Osa peninsula, a peninsula in Costa Rica

Osa, Perm Krai, a town in Perm Krai, Russia

Open Services Architecture

M79 Osa, an Eastern Bloc rocket launcher

The Office of Special Affairs, a controversial department of the Church of Scientology

Open Systems Adapter an IBM Card for Mainframe

Ordo Sancti Augustini (Order of Saint Augustine), the Roman Catholic Augustinian order

Oakland School for the Arts an arts high school in Oakland, California.

Orissa Society of the Americas a non-profit organization that promotes understanding of Oriya culture and history.