As with any industry, there are lots of new confusing words and sublimation is no different.
The substrate is the thing you transfer to like a mug and mouse pad.
One of the most common materials for sublimation, is Unisub FRP. Unisub is sort of the name that coates this product. Their real name is Universal Woods located in Kentucky. FRP is short for Fiber Reinforced Plastic or Fiberglass. This substrate is cut into many different sizes and shapes like license plates and luggage tags.
It sublimates beautifully!
Here is my video with some great info about Unisub FRP: