What Is a Tuffet?
In the "Little Miss Muffet" rhyme, the titular character is said to sit on a tuffet, which can be seen either as a tufty clump of grass or a small stool similar to a pouffe. However, because Miss Muffet is said to be frightened away from her seat by a spider, it may be safe to assume that, in this context, the referenced tuffet is a clump of grass rather than a piece of furniture.
The origins of the use of the word "tuffet" to describe furniture seems to be related to the use of the word to describe an inviting clump of grass. The exact meaning in the context of the rhyme seems to be up to interpretation.