An oyster knife is a short-bladed, dull knife designed shuck oysters. The tip is flat and pointed enough to penetrate the tightly closed hinge of an oyster shell, but rounded enough on the tip that it doesn't cut into the oyster's flesh.

Even though its blade isn't sharp, an oyster knife can be dangerous. When shucking an oyster the knife is usually pointed toward the hand that holds the oyster as you're trying to pry open the shell with the knife. Guard against slipping by protecting your hand with a stainless steel-mesh glove or a kitchen towel.

Reference: How to choose oysters
Reference: How to shuck an oyster