This root word is used in many words related to sound and three-dimensional space:
* Stereoscopic vision: The ability to perceive depth, based on the slightly different images seen by each eye.
* Stereophonic sound: The reproduction of sound in a way that simulates the natural spatial distribution of sound sources.
* Stereotype: A widely held but fixed and oversimplified image or idea of a particular type of person or thing. (In this case, the "solid" meaning relates to the fixed and unchanging nature of a stereotype.)
So, while "stereo" may initially sound like a word related to sound, its deeper meaning refers to the solidity, firmness, or three-dimensional nature of something.