1. When somebody approves of something which they think is really cool or down. In fact, 'San' is so cool itself it cannot be defined accurately. The pure essence of 'San' cannot be contained within a physical form, for it is ethereal and a part of many things.
2. It can also be used to greet a person, in place of certain trivialties as 'hello', or 'safe', for example.
3. It can be used in place of a word to, ironically show ones gratitude for it.
(The elongation of the word 'San', i.e. 'Saaaaaan' merely extends the emphasis of whichever context it is used in.)
1. Person 1: Hey I just found a £20 note on the floor.
Person 2: San!
2. Person 1: Alright man, how's it going?
Person 2: San.
3. Person 1: Hey would you like some whiskey?
Person 2: Surely you mean some san. That whiskey is pretty beasty.