A material that does not allow light to pass through it is known as what?

A material that does not allow light to pass through it is referred to as opaque. The term "opaque" specifically indicates that light cannot penetrate the material, making it impossible to see through. This characteristic is important in various applications, such as construction or design, where light blockage may be desired.

Transparent materials, on the other hand, allow light to pass through with little to no obstruction, enabling clear visibility. Translucent materials permit some light to filter through but obscure clarity, providing a blurred effect. The term "illuminating" is unrelated to the properties of materials concerning light transmission, as it refers to the act of providing or enhancing light rather than describing how a material interacts with light. Thus, opaque accurately describes a material that prevents light from passing through.