What is Ossu?
1.
1) informal greeting way among young male friends. Should not be used to greet older people.
2) Some Karate practicing people may be using this term in place of such as "yes sir*. However, it seems this word is a recent invention and not so much used among degnified old Karate-ka.
1) When two boys meet, they may say "ossu" "ossu" like "Hi" "Hello".
2) Karate-ka 1 show example, another may say "ossu".
See
2.
"Hi" in Japanese, informal
it's okay to use ossu with friends.. but not really with people of high status =P
See