concentric

A concentric shape is one that has circles or other shapes inside each other. Think of a ring with another smaller ring inside it.

Concentric is often used to describe things that are connected or related but also separate from each other. For example, if you're talking about the different layers of the Earth's atmosphere, like the troposphere and the stratosphere, you might say they have concentric shapes because one layer fits snugly inside the next. Scientists use this word a lot when studying geology and astronomy to describe how different parts fit together.