Slang. In
drug circles, a
bump is a small amount of a substance that you plan on inhaling. For instance, rather than
snorting a whole
line of
coke, you can take the edge of your
credit card/
drivers license/
key/etc dip it into the larger pile of white, and bring the smaller pile you've scooped up to your nose, and sniff.
Voila! That's a
bump.