A verb, noun, adjective or adverb without definition. It can be used as a replacement for other slang terms, pejorative or meliorative, and can be altered to suit the situation.
Basically it's a word that can mean whatever you want, and in that sense is similar to the word 'fuck'.
Amelia said, "That party was ranging!"
Barry whispered to Laurence, "You smell ranging..."
John laughed heartily, "Last night I was ranged off my nuts!"