Bug
Bug may refer to:

 Bug (defect), a computer or hardware defect found in a device that needs fixing
 Bug (device), a type of covert listening device
 Bug (illness), a colloquial term for an illness caused by a virus or other microorganism
 Bug (invertebrate), a colloquial term for any insect, arachnid, or other terrestrial arthropod that is a pest
 Insect, what "bug" often seems to refer to