Count : To count means to find out the number of objects by adding one for every object.

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

Number : A number $x$ is a mathematical symbol representing a quantity.

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 $cm.$

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 : A square is a quadrilateral with four right angles and four equal length sides. A square is a special case of a rectangle and a special case of a rhombus.

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 $m^2.$

Subtraction : Subtraction is the mathematical operation that describes decreasing a number by an amount equal to a second number. The mathematical symbol for subtraction is the minus sign $-.$ The term subtraction is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

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.

Counterexample : A counterexample to a statement of the form 'all objects of type x have property y' is an object of type x that does not have property y. A counterexample to a statement shows that the statement is not true in general. For example the number 3 is a counterexample to the statement that all numbers are even.

Multiplication : Multiplication is the mathematical operation that is a shorthand for adding the same amount several times. For example $3\cdot 4=4+4+4=12.$

Natural number : A natural number is any of the numbers 1,2,3,...

Subtraction : Subtraction is the mathematical operation that describes decreasing a number by an amount equal to a second number. The mathematical symbol for subtraction is the minus sign $-.$ The term subtraction is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.