A word one uses when they have nothing else to say. It's also used in replacement of different words to make it sound more interesting. Commonly used to replace swear words, making a conversation more entertaining.
some1:ur such a pendejo!
some1else:psh!
person:psh u!!!
bob: u needalot of pshing help u pshing son of a psh!
me:pshpshpshpshpsh!
ray:u've gone over the psh limit gurl!
The sound you make that signifies that a specific person has sex appeal, and that you would tap that.
It is usually accompanied by a hand gesture, which is a slapping motion to show that you'd hit it from behind aka doggystyle. (pretending to slap someone's ass)