Pronunciation: (drop'in"),[key] —n. 1. Informal.Also,dropper-in.a person who or thing that pays an unexpected or uninvited visit: a feeder for squirrels, raccoons, and other drop-ins. 2. Informal.a social gathering at which the guests are not expected to stay long: Be sure to stop by our house for a glass of eggnog at our Christmas drop-in.
—adj. 1. provided for short-term patronage: a drop-in shelter for the homeless. 2. requiring only insertion to be ready for use: a drop-in film cartridge.