The name derives from an idiomatic English metaphor which asserts that nervous, fidgety people must have "ants in their pants." The English word "antsy" (meaning nervous) also derives from this metaphor.
The fundamental pieces involved in Ants in the Pants are a free-standing pair of miniature, usually plastic, pants; and several plastic ants. The ants are color coded - each player uses one color of ants - and designed so that pressing the tail stores elastic potential energy. When the tail is pressed and released, the ants spring into the air.
The object of Ants in the Pants is to spring as many of your ants as possible into the pants.
Some versions of Ants in the Pants include characters which "wear" the pants. These (usually cardboard) cutouts depict the character, and also serve as backboards to deflect the ants into the pants. Plastic suspenders (or braces) are another common element, which serve as obstacles.