All true drums belong to the Membranophone family of instruments. They are instruments in which sound is made by the vibration of a stretched membrane or skin. They are classified on this website according to their body shapes. Some instruments that are commonly called drums (i.e. steel drums, kettle drums) are made entirely of resonant solid material and would be classified as Idiophones.
The Membranophone family of instruments consists of two basic groups: drums and mirlitons. Mirlitons are instruments that use a vibrating membrane to modify the sound made another way. Usually it is activated by blowing or singing against it. A Kazoo is an example of a Mirliton.