You will learn this in geometry.
Concentric means "sharing the same center". Con- = used multiple times, -Centric = center-related. (like cooperate: multiple people doing the same task)
So, it's like a dartboard or bullseye: the circles are all around the same point.
Something three-dimensional, like cylinders (water bottles, spray cans), may be coaxial
The solar system is concentric. All the planets orbit the sun.
A properly set table has the bowls and plates concentric.