When you flick a coin so that it slides across a table, it slows down.

what is the name of the force that slows it down

Well it depends on the coin and the tables material, a table is a bit too broad, either what i know could be friction force between the table and the coin or air resistance force. not sure about gravity force

Sorry not sure

Gravity is acting on every object, but friction between the two objects is the resisting force causing the coin to slow it's horizontal motion across the table surface.