Concentric

Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another. Concentric objects do not generally have the same radius.

Examples of concentric phenomena
Concentric cable is a cable type used in TN-C-S earthing systems where the combined neutral and earth core completely surrounds the live core(s). This minimises the risk of completely cutting through the combined neutral and earth without first completely cutting through the live cores.

Concentric muscles contractions are those in which the muscle shortens.