A Platonic solid is a 3D shape that meets three main requirements:

1. All the faces must be equal and they need to be regular polygons
2. The same number of faces must meet at each vertex
3. The shape must be convex — for example, it can't be something like a star

Only five solids meet the criteria: tetrahedrons, cubes, octahedrons, dodecahedrons, and icosahedrons.