Pocket pet is a term used to refer to any small mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

 commonly kept as a household pet

Pet

A pet is a household animal kept for companionship and a person's enjoyment, as opposed to wild animals or to livestock, laboratory animals, working animals or sport animals, which are kept for economic or productive reasons. The most popular pets are noted for their loyal or playful...

. The six general criteria which qualify an animal to be considered a pocket pet are:

1. its commonality as a domestic housepet
2. no potential danger to humans or other animals
3. non-exotic
4. overall ease of care and feeding
5. amicable disposition making it suitable as a "companion" pet
6. relatively small stature

The most common pocket pets include rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

s such as: hamster

Hamster

Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....

s, gerbil

Gerbil

A gerbil is a small mammal of the order Rodentia. Once known simply as "desert rats", the gerbil subfamily includes about 110 species of African, Indian, and Asian rodents, including sand rats and jirds, all of which are adapted to arid habitats...

s, fancy mice

Fancy mouse

Fancy mice are domesticated breeds of the common or house mouse . The terms fancy and "feeder mice" are often used interchangeably by retailers, and are in fact the same variety of mouse....

, fancy rat

Fancy rat

The fancy rat is a domesticated brown rat , which is the most common type of pet rat. The name fancy rat derives from the idea of animal fancy or the phrase "to fancy" ....

s, guinea pig

Guinea pig

The guinea pig , also called the cavy, is a species of rodent belonging to the family Caviidae and the genus Cavia. Despite their common name, these animals are not in the pig family, nor are they from Guinea...

s and hedgehog

Hedgehog

A hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand . There are no hedgehogs native to Australia, and no living species native to the Americas...

s. It also includes pets such as sugar glider

Sugar Glider

The sugar glider is a small gliding possum originating from the marsupial family.The sugar glider is native to eastern and northern mainland Australia and is also native to New Guinea and the Bismarck Archipelago.- Habitat :Sugar gliders can be found all throughout the northern and eastern parts of...

s,flying squirrels etc.; which have been bred as domestic housepets in the U.S. for the last 15 years.