What is the meaning of Guinea_pig?

A tailless rodent of the family Caviidae and the genus Cavia, with short ears and larger than a hamster; the species Cavia porcellus is often kept as a pet.

A rodent of any of several species within the family Caviidae.

A living experimental subject.

A professional company director, without time or real qualifications for the duties.

A midshipman in the East India service; a low-skilled or non-proficient seaman.

Source: wiktionary.org