1. The problem is to understand what "congruent" means in mathematics. 2. In math, two figures or numbers are called congruent if they have the same shape and size or if they are equal in value. 3. For example, two triangles are congruent if all their corresponding sides and angles are equal. 4. In number theory, two numbers are congruent modulo $n$ if they leave the same remainder when divided by $n$. This is written as $a \equiv b \pmod{n}$. 5. So, congruence means equality in shape and size for geometry, or equality in remainder for numbers under modular arithmetic. 6. It is a way to say two things are "the same" in a specific mathematical sense.