What is 5²?

To determine what 5² is, we need to understand the concept of exponentiation. The notation 5² means "5 raised to the power of 2." This means that we take the number 5 and multiply it by itself:

5 × 5 = 25.

Thus, 5² simplifies to 25. This calculation shows the fundamental property of exponents where the base (in this case, 5) is multiplied by itself as many times as indicated by the exponent (which is 2).

Therefore, the correct answer is indeed 25.