Simple Definition:

In math, “congruent” means that two objects have the same shape and size.

For example, if two triangles have the same side lengths and angles, they are congruent. Or if two circles have the same radius, they are congruent.

Very Simple Definition:

Congruent means that two things are exactly the same in shape and size.

For example, if two squares look exactly alike and have the same size, they are congruent.