Slang used to denote a gay male who likes animals, either as an animal lover, or sexually.
It can simply refer to a gay male, who likes animals, as pets, or as a species to enjoy, in a non sexual way.
It can also refer to someone who desires to have sex with an animal, any animal, and is a slang term for Zoophilia or bestiality.
Noteworthy: Zoo Queens may not actually engage in sex with animals, but have that desire or discuss it frequently.
Sex with animals is a criminal act in most countries.