OSS!

OSS (actually OSU!) is a phonetic expression, formed out of two characters. The first character OSU means literally push or control and determines the pronunciation of the whole term. The second character SHINOBU has the literal meaning of bear, endure, suffer. 
 

The expression OSS was created in the Japanese Naval School and is universally used for everyday expressions such as please, thank you, I understand, sorry, greeting someone, etc., as well as inside the world of Japanese martial arts nearly any time a response is required.
 

OSS must not be said loosely, OSS should be spoken by using the hara (tanden), in the lower abdomen. Spoken while performing a bow with the upper third of the body, the word OSS expresses respect, sympathy and confidence in the partner. OSS also tells the sensei that the instructions were understood and that the student will do his/her best to follow them.

In the following situations OSS should be used:

A- When bowing at the start and finish of the class.

B- Upon receiving any advice or command from the Instructor, the student must reply by answering OSS .

C- Before and after Randori or Kata.

D- Upon receiving OSS from Instructors.