Longman Dictionary of Contemporary English
Wiktionary
a. 1 provided for short-term use 2 (context industry English) fit to substitute some element in a complex system without changes to the existing infrastructure n. 1 one who casually drops in. 2 informal social event
Wikipedia
Drop-In was a Canadian television series for youth broadcast on CBC Television from 28 September 1970 to 1974. Various hosts were featured throughout the course of the series to present a variety of topics.
The show was broadcast three times per week in the 1970-1971 season. This was increased to four times per week in the following year.
Usage examples of "drop-in".
The Port Dutch was a midtown hotel for millionaires of all kindsoil sheiks, arbitrageurs, rock legends, British royalsand its suites, two per floor facing Central Park across Fifth Avenue, almost always repaid a drop-in visit during the dinner hour.
And after much commiseration on the subject, it had already been decided that Jasmine was going to do it, but to alleviate her fears, it was also decided that she need take no new bookings and only fulfill those already made, and maintain the house for those drop-ins who came to see the site of their engagements or weddings, et cetera, or merely to visit the pretty house about which they had read in the guides.
Malone and Clements, in suits and hats and ties, not a muscle in sight, looked like drop-ins from another planet.
The Smokies shelters are supposed to be for thru-hikers, not casual drop-ins, and words were sometimes exchanged.
They were strollers and drop-ins, tourists and islanders alike who had come down to the bay for a late-night drink or something to eat and to look out at the forbidding statues repelling whatever malign spirits might at any moment emerge from the sea.
Now she works in a drop-in business shop, stacking shelves for virtual fly-by-nights that come and go like tourists in the Festival season—but humans aren’t in demand for shelf stacking either, these days.