Area : The amount of unit squares that is needed to cover a 2-dimensional shape.

Centimeter : A centimeter ($cm$) is $\frac{1}{100}$ of a meter.

Equation : An equation is a mathematical statement in which two expressions are written with an equal sign in between. A solution of an equation is a set of variables that makes the statement a true statement.

Length : Length is the attribute of a one-dimensional shape that can be measured with a measuring tape.

Liter : A liter is a unit for measuring volume. A liter is the volume equal to the volume of a cube with side length 10 cm. 1 liter equals $1,000 cm^3.$

Perimeter : The perimeter of a two-dimensional shape is the length of the boundary of the shape. For a polygon this is the same as the sum of all the side lengths. For example a triangle with side lengths 1, 2 and 3cm has a perimeter of 1+2+3=6cm. The perimeter of a circle is referred to as its circumference.

Plus : Plus is either a symbol or another word for addition.

Rectangle : A rectangle is a quadrilateral with 4 right angles. Two opposing sides in a rectangle have the same length. They are sometimes referred to as the width and the length of the rectangle. To calculate the area of an rectangle one can multiply the width of the rectangle by the length of the rectangle. A square is the special case of a rectangle in which all side lengths are the same. Every rectangle is a parallelogram.

Square centimeter : Square centimeter or $cm^2$ is a unit of measurement for measuring area. 1 square centimeter is the area of a square with side length 1 $cm,$ so 10,000 $cm^2$ are one $m^2.$