Rodents are mammals which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. This would normally include rats, mice, beavers, and porcupines.
In patch 7.3.0 the porcupine hunter pet family was renamed to rodent to include more types of animals.
As a hunter pet
Rodents are a family of tenacity pets and are tamable by hunters starting at level 84. They like to eat fungus.
In World of Warcraft the classification only includes:
Patch 7.3.0 (2017-08-29): The pet family name was renamed to rodent, from porcupine, in order to include more creatures.
Patch 6.0.2 (2014-10-14): [Paralyzing Quill] replaced with [Defensive Quills].
Patch 5.0.4 (2012-08-28): Added.