Definitions of bug:

noun: general term for any insect or similar creeping or crawling invertebrate
noun: a small hidden microphone; for listening secretly
noun: a fault or defect in a system or machine
noun: a minute life form (especially a disease-causing bacterium); the term is not in technical use
noun: insects with sucking mouthparts and forewings thickened and leathery at the base; usually show incomplete metamorphosis
verb: tap a telephone or telegraph wire to get information
Example: "Is this hotel room bugged?"
verb: annoy persistently