What is the area of a square with a side length of 5 units?

To find the area of a square, the formula used is ( A = s^2 ), where ( s ) is the length of one side of the square. In this case, the side length is given as 5 units. By plugging this value into the formula, you calculate the area as follows:

[ A = 5^2 = 5 \times 5 = 25 \text{ square units}. ]

Thus, the area of the square is 25 square units, which matches the choice provided. This demonstrates that when you're dealing with squares, squaring the length of a side directly gives you the area, highlighting the fundamental geometric principle related to squares.