Here go a definition if you want some details to Jmaafia's reply
From the Dallas symhony orchestra.
The snare drum joined the orchestra nearly 200 years ago. It has two calfskin or plastic drumheads stretched tightly over a hollow metal frame. The top head is struck with wooden drumsticks, and is called the batter-head. The bottom head, or snare-head has catgut or metal wires called snares stretched tightly across it. When this untuned drum is struck on the top head, the snares produce a characteristic sharp rattling sound as they vibrate against the bottom head.