OSS
OSS it's a pretty generic term derived from Japanese martial arts. It is a particularly enthusiastic way of saying “yes” or to acknowledge something or someone, similar to the U.S. Marines when we say “OOH-RAH”.

The famous “OSS” has many origins. The first definition of “OSS” as an abbreviation for Onegai Shimasu, which translates into a request, a solicitation, an invitation like “please”, “if you may” or “with your permission”, much used when inviting a partner to train.
Sensei: Are you ready?

Kouhais: OSS!