Tile
From Brickwiki
A tile can be described as a plate without studs on top of it.
Tiles are commonly decorated with printing or stickers. The smooth surface makes such decoration easy and allows for details that would otherwise not be possible building with plain coloured elements.
Most tiles are produced in either 1x or 2x sizes. This refers to the width in studs and is a common shorthand when describing the measurement of a LEGO model or element.