What is the difference between equal and congruent

When something is equal to something else, they are both the same in either one or more ways.

When something is congruent to something else, they are always exactly the same.

Example:

Identical twins are congruent because they are the same in every way. Their age, their appearance.

Fraternal twins are equal because they are the same in some way. Their age is the same, but they look different.