In short, a polyhedral die is any die that has multiple faces, all of which are equal in size to each other. There are many kinds of polyhedral dice. The most common of which is perhaps the six-sided die found in common games like Yahtzee or Backgammon. Polyhedral dice can have as few as three sides and as many as one hundred.

Polygons have at least three straight angles and sides and are two-dimensional shapes. Any diye that has multiple faces is a polyhedral die. Additionally, the faces are equal to each other in size. The most common kinds of polyhedral dice are probably the six-sided sets used in backgammon or Yahtzee.

"a three-dimensional solid which consists of a collection of polygons, usually joined at their edges" By this definition all dice fit into this category For purposes of this category... polyhedral dice are actually the Platonic Solids plus the Pentagonal Trapezohedron