An very sensitive yet powerful explosive. Common applications include a really cool-looking cloud of dust (yay!) and setting off even more powerful explosives. Referred to as AP.
Be careful using the acronym AP at school because it also stands for Advanced Placement which is something completely different :P
It's also dangerous to make if you're not being careful.
Guy 1: Why is there a hole in my basement?
Guy 2: I messing around with some AP...
Guy 1: Advanced Placement?
Guy 2: No, Acetone Peroxide. Why would a test blow a hole in your basement?