What is Piss ?
Piss is (offensive slang) (noun) 1. liquid waste from the body. Synonym urine to take the piss to make fun of someone I thought he was taking the piss, but he was deadly serious. 2. the act of passing waste water from the body I must go and have a piss. (verb) to pass waste water from the body. Synonym urinate
source: Easier English, Student Dictionary Upper Intermediate Level