What is the bump of skin at the behind the back tooth?

Answer:

Part of the gum. - http://en.wikipedia.org/wiki/Gum_(anatomy)

If it is enlarged, there is probably a problem with the teeth/gums, go see your dentist.

First answer by Benche. Last edit by Benche. Contributor trust: 5 [recommend contributor recommended]. Question popularity: 1 [recommend question].