What is the meaning of Guinea_pig?

Any tailless rodent of the genus Cavia, which have short ears and superficially resemble large hamsters.

1. A domestic guinea pig, Cavia porcellus, often kept as a pet.

   A domestic guinea pig, Cavia porcellus, often kept as a pet.

   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