A "creem deem" is a slang term used to describe a large amount of cannabis smoke that is inhaled via a bong/water pipe. The smoker will light the bowl and slowly inhale for a long period of time. The smoke in the pipe accumulates and quickly turns milky white as it becomes more and more dense. This is called a "creem deem".
"OMG! Check out that creem deem in john's tube."
"Ohhh that ones definately a creem deem!"