Tom drums were first used by jazz drummers in the 20th Century. The original toms had no rims and drummers tuned them using the heat from a match and some water. Modern toms have proper rims and tuning lugs and are made of a shell, head, and metal hardware.
Tom drums are distinctive because they are double-headed but have no snare. They are built in a variety of different depths and diameters in order offer a wide range of timbre. Two rack toms are considered standard for most drum sets.
Mounting systems for tom drums vary on the setting and type of tom you are playing. Most are designed to mount on a rack, but others are designed to hang from a marching harness, or have their own freestanding stand.