A thrust washer is a flat washer like a normal washer but the difference is the thrust washer has ball bearings that allow rotation and are located between a rotating surface and a stationary component.
The thrust washer supports an axial load or side to side motion on a shaft and prevents movement along a shaft.
Thrust Washers provide a surface on to which a bearing is supported.
A thrust washer is also known as a thrust bearing in which a flat bearing is sandwiched between two flat washers or even some thrust washers are simply a washer with a built in bearing that allows movement.
Another way to spot a thrust washer is to look for a flat bearing that looks like a washer but the inside of the washer is a bearing that spins around.
However some thrust bearings are just a flat bearing and then you put one regular washer on top and another washer on the bottom of it.