Drop-in

Full definition of drop-in

Adjective

1. provided for short-term use
2. (industry) fit to substitute some element in a complex system without changes to the existing infrastructureWe need the ultimate drop-in biofuel to make use of our expensive oil-based infrastructure.
• 2012, Robert Mendelsohn, Ariel Dinar, Handbook on Climate Change and Agriculture, page 276An alternative to cellulosic based second- generation biofuels are drop-in biofuels, that is, fuels such as synthetic gasoline that can be put into fuel tanks and pipelines with no modifications.

Noun

1. one who casually drops in.
2. informal social event