"Whether in real life or Sanctuary, no one wants to wait around while you pick out which pants to wear."(src)
"Pants guarantee a few easily accessible pockets to tuck gold and knives. With increasingly potent shielding, they can also prevent hamstrings and calves from being torn free."— Game Guide(src)
Pants are a type of armor items introduced in Diablo III. They protect and cover legs, and have at least some degree of changing appearance (that is, can be transmogrified). However, pants affect your appearance much less than Body Armors. Interestingly, all Demon Hunter pants have quivers attached to them, which are actually shown on character model.
In addition to all-armor and core stats, pants may roll other defensive bonuses: Armor, resistances, up to two sockets, Life per second, Life per Kill, Thorns, chance to Slow on hit and gold / health pickup radius. They can also roll increased damage for primary skills.