drop-in

[drop-in] /ˈdrɒpˌɪn/
noun
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.
adjective
3.
provided for short-term patronage:
a drop-in shelter for the homeless.
4.
requiring only insertion to be ready for use:
a drop-in film cartridge.
Origin
1810-20; noun, adj. use of verb phrase drop in
Examples from the web for drop-in
  • There's no food service, but a dozen tables and chairs encourage drop-in tasters.
  • Homemade candy is wonderful to have on hand for nibbling or offering to drop-in guests.
  • The difference in density and distillation curves of the different drop-in biofuels are presented.
  • There are a number of critical ingredients to running a successful drop-in center.
Slang definitions & phrases for drop-in

drop-in

noun
  1. A place of temporary and sometimes dubious resort: drop-ins for youths wishing marijuana revels (1950s+)
  2. A person who attends classes and other college events without being registered: NBC did some research on college drop-ins (1960s+ Students)
  3. A new car engine as a replacement: If you have a current model-year car, you can get a ''drop-in.'' That's a brand new engine (1990s+)

[sense 2 is the opposite of a dropout]