dropdown
noun
Definitions
An instance of a selection object that hides the contents (especially the other choices) until activated.
Example: That screen is good, but add a couple of dropdowns and it will be perfect.
adjective
Definitions
(of a widget) Dropping down from above; being a specific type of selection control that hides its contents until activated.
Example: Click the Colours button on the toolbar to show a dropdown menu of available colours.