What is a snakebite?

Snakebite on a bicycle: A flat tire where the holes look like they have been bitten by a snake.

Snakebite - snake bite:
 A flat tire where the holes look like they have been bitten by a snake. These holes in the tube are caused by riding your bike over an edge and the edge, root, etc. has pressed the tire and tube together so hard that the edge has come up to the rim and thus caused the holes.

Relevant articles:
Inflate bicycle tires , change bicycle tubes and bicycle tires