What does it mean for two objects to be concentric?

When two objects are described as concentric, it means that they share a common center. This concept is often applied to circular objects, such as circles or cylinders, which may have different radii but are centered around the same point. The sharing of a common center can be important in various applications, such as in the design of gears or in the alignment of components in machinery, ensuring that they function efficiently together.

The other options do not accurately capture the meaning of concentric. For instance, saying that two objects occupy the same physical space would imply overlap, which is not a requirement for concentricity. Being attached to one another indicates a physical connection rather than a shared center. Lastly, being parallel relates to the directional alignment of objects, not their central positioning. Thus, the characteristic of sharing a common center is essential to defining concentricity in any context involving circular or cylindrical objects.