Transparent, translucent, and opaque describes how visible light passes through a material.
A transparent material allows visible light to pass through it. Some of the light may be absorbed, but it is possible to see objects through the material. Familiar examples of transparent materials are air, water, some plastics, and clear glass.
Translucent materials allow some light through them but it is scattered so it is impossible to see a clear image through the material. Examples of translucent materials are some plastics and frosted glass.
Opaque materials don't let light through them at all. The light is either reflected or absorbed. Absorbed light heats up the material. Examples of opaque materials are stone, metals, and some plastics.
The terms are meant to describe visible light. For example, clear glass is transparent to visible light but opaque to ultraviolet light.