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 defined as opaque. This means that when light hits the surface of an opaque material, it cannot penetrate it; instead, that light is either absorbed or reflected. Common examples of opaque materials include metals, wood, and certain types of plastics.

The other terms relate to how materials interact with light: transparent materials allow light to pass through completely, which enables clear visibility of objects on the other side. Translucent materials permit some light to pass through but scatter it, resulting in a blurred image of objects behind them. Illuminating, while related to the emission of light, does not specifically refer to the property of transmitting light through a material. Thus, the definition of opaque appropriately describes the intended characteristic of not allowing light passage.