What is the name of the old-time, handheld toy that consists of a plastic frame with scrambled, notched letter or number tiles?

Isn't it just "Sliding Tiles" or "Sliding Tile Puzzle", Lexi?

There's also a version (with which I'm more familiar, and which is more for kids, perhaps) where you end up with a simple picture. I think this is known as (fanfare) a "Sliding Picture Puzzle".