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

Common denominator : The common denominator of two or more fractions is a number that is a multiple of all the denominators of the fractions. For example 12 and 24 are both common denominators of $\frac{3}{4}$ and $\frac{1}{6}.$

Denominator : The denominator of a fraction $\frac{a}{b}$ is the number $b$ below the fraction bar.

Equivalent fraction : Equivalent fractions are fractions that represent the same number. For example the fractions $\frac{1}{2}$ and $\frac{2}{4}$ are equivalent. One can create equivalent fractions of a fraction by multiplying or dividing both the numerator and the denominator of the fraction by the same non-zero number.

Fraction : A fraction is a number that can be written as $\frac{a}{b}$ with an integer $a$ and a natural numbers $b.$ A fraction $\frac{a}{b}$ is the result of the division $a\div b.$ Examples of fractions are $\frac{1}{2}, -\frac{2}{3}$ and $\frac{3}{2}.$

Numerator : The numerator of a fraction $\frac{a}{b}$ is the number $a$ above the fraction bar.

Positive : Positive means $\geq 0.$

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.

Angle : If two line segments (or rays) both start at a common point the opening between the two line segments is called an angle. The common point is called vertex of the angle. The size of an angle is measured in degrees.

Line : A line AB is a one-dimensional shape that includes the points A and B, all the points on the line segment in between A and B and all the points of the straight extension of the line segment beyond A and B. A line does not have an endpoint.

Parallel : Two lines in a two-dimensional plane are called parallel if they never cross.

Perpendicular line : Two lines are called perpendicular if they cross in a right angle.

Point : A point is an element in a space. Shapes are made of sets of points.

Right angle : A right angle is an angle equal to $90^{\circ}.$