What is a 100 sided 3D shape called?

A 100-sided 3D shape is called a hectohedron.

Here’s the detailed explanation:

Terminology: In geometry, a "hedron" refers to a 3D shape, and the prefix "hecto-" denotes 100. Combining these gives "hectohedron."

Regular vs. Irregular:

If all 100 faces of the shape are identical and regular polygons (such as equilateral triangles or squares), the shape is a regular hectohedron.
If the faces vary in shape or size, it is an irregular hectohedron.
Practical Examples:

Regular hectohedra are theoretical and highly symmetrical.
Irregular hectohedra could be created in practical scenarios, such as in computer graphics or modeling, by assembling 100 polygonal faces in a 3D space.
Note: The term is rarely used because shapes with such a high number of faces are more commonly described in specialized contexts rather than in standard geometry.