CCSS.Math.Content.3.MD.C.5 Recognize area as an attribute of plane figures and understand concepts of area measurement.

• CCSS.Math.Content.3.MD.C.5a
  A square with side length 1 unit, called "a unit square," is said to have "one square unit" of area, and can be used to measure area.
• CCSS.Math.Content.3.MD.C.5b
  A plane figure which can be covered without gaps or overlaps by n unit squares is said to have an area of n square units.