• The surface area of a figure (in square units) is the number of unit squares it takes to cover the entire surface without gaps or overlaps.
• If a three-dimensional figure has flat sides, the sides are called faces.
• The surface area is the total of the areas of the faces.

So the surface area of a rectangular prism that has edge-lengths of 2 cm, 3 cm, and 4 cm has a surface area of

$\displaystyle (2\boldcdot 3)+ (2\boldcdot 3) + (2\boldcdot 4) + (2\boldcdot 4) + (3\boldcdot 4) + (3\boldcdot 4)$

or 52 square centimeters.