any of a genus (Musca) of disease-carrying muscid flies found in and around houses, and feeding on garbage, manure, and food; esp., a common worldwide species (M. domestica)
See housefly in American Heritage Dictionary 4
noun
A common, widely distributed fly (Musca domestica) that frequents human dwellings, breeds in moist or decaying organic matter, and transmits a wide variety of diseases.