Circle : A circle is a two-dimensional shape. The boundary of a circle is a set of points that has the same distance (the radius) from the center of the circle.

Cube : A cube is a three-dimensional shape with 6 faces that are all squares. A cube has 8 corners and 12 edges.

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.

Shape : A shape is a set of points in space.

Sphere : A sphere is a three-dimensional shape that has a boundary equal to a set of points with a constant distance to a point. The point is called the center of the sphere and the distance is called the radius $r$ of the sphere. The volume of a sphere with radius $r$ is $\frac{4}{3}\pi r^3$ and the surface area is $4\pi r^2.$

Three-dimensional : An object or vector is called three dimensional if it has a width, length and depth or a one-to-one mapping to an object or shape that has a width, length and depth.

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

Inch : An inch or $in$ is a unit of measurement for length. 12 inches are one foot and 1 inch is about 2.54 $cm.$

Square inch : Square inch is a unit of measurement for measuring area. 1 square inch is the area of a square with side length 1 inch. 144 square inches are 1 square foot.

Addition : Addition is the mathematical operation that describes increasing a number by an amount equal to a second number. The mathematical symbol for addition is the plus sign $+.$ The term addition is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

Sum : A sum is the result of an addition.

Summand : A number in a sum is called summand.

Term : If an expression can be written as a sum of several parts we call these parts terms.

Third : A third either refers to the third object in an ordering or to the number $\frac{1}{3}=0.\overline{3}.$