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.

Zero : The number 0.

Decimal point : The point in a decimal separating the digits representing multiples of wholes from the digits representing fractions of wholes.

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.

Alternate interior angle : When two parallel lines are crossed by a third line, alternate interior angles are a pair of angles that are between the two parallel lines and are on opposites sides of the crossing line. Alternate interior angles are equal.

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.

Straight angle : A straight angle is an angle equal to $180^{\circ}.$