Lost Pets
The term of lost pets refers to animals or mobs that were at some point tamed or owned by an individual who has since abandonned them. This can happen either when a player becomes inactive, moves away or more commonly when they die. Lost pets can mainly be found near spawn with dogs being the most frequently found pet.
Context
A few animals in Minecraft are directly tied to the person that has tamed them with no way to be untamed or given to another player. These include cats, dogs and parrots. As such, when the original owners of these pets go missing, they become stuck, sat for eternity.