Noun
pet rock (plural pet rocks)
A rock one keeps and cares for as if it were a pet, often purchased as a novelty item and jokingly treated as having needs like those of a living animal.
There are also inanimate objects that have been kept as "pets", either as a form of game, or humorously (e.g. the Pet Rock or Chia Pet ). Source: Internet
How Did the Pet Rock Fad Start? Source: Internet
Next year they could be the new Pet Rock. Source: Internet