A spacer is a thin and often tapered or wedged piece of material, used to fill small gaps or spaces between objects. Spacers are typically used in order to support, adjust for better fit, or provide a level surface. Wedges may also be used as spacers to fill gaps between parts subject to wear.
At glance: Tile Levelers
A T shaped support that sits on the floor with the base of the T extending up which has an opening in it to except a wedge . By applying pressure to the wedge it will squeeze the 2 tiles to a level plain eliminating lippage.
Popular brands of tile spacers available at Prefloortools.com include QEP, Spin Doctor, Lash Clips