The guinea pig or domestic guinea pig, also known as the cavy or domestic cavy, is a species of rodent belonging to the genus Cavia in the family Caviidae. Breeders tend to use the name "cavy" for the animal, but "guinea pig" is more commonly used in scientific and laboratory contexts. Despite their name, guinea pigs are not native to Guinea, nor are they closely related to pigs. They originated in the Andes region of South America. Studies based on biochemistry and hybridization suggest they are domesticated animals that do not exist naturally in the wild, descendants of a closely related cavy species such as C. tschudii. They were originally domesticated as livestock for a source of meat, and are still consumed in some parts of the world.

Rodents are mammals of the order Rodentia, which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are native to all major land masses except for New Zealand, Antarctica, and several oceanic islands, though they have subsequently been introduced to most of these land masses by human activity.