In a 1956 Remington folder on Parker parts it is referred to as a trigger plate. This is very similar to the parts illustration that can be seen from the home page under technical information but I do not believe it to be the same which refers to it as a trigger plate as well.
Then there is the definition of Floorplate as taken from Hallowells Firearm dictionary as follows: "Floorplate - A cover, usually of metal, usually hinged and latched, on the bottom of a bolt action rifle action which, when opened, allows the internal magazine to be emptied."
