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.

Corner : A corner of a shape is a point in the shape such that this point does not lie on the line segment between any two other points in the shape. Every triangle has 3 corners and every quadrilateral has 4 corners.

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

Quadrilateral : A quadrilateral or quadrangle is a polygon with four corners. Rectangles, trapezoids, kites, rhombuses, squares and parallelograms are all specific kinds of quadrilaterals. The sum of the interior angles in a quadrilateral is always $360^{\circ}.$

Kilometer : A kilometer is a unit for measuring length equal to 1,000 meters.

Millimeter : A millimeter is a unit for measuring length equal to $\frac{1}{1000}$ of a meter.

Million : A million refers to the number $1,000,000={10}^6.$

Thousand : Thousand refers to the number $1,000=10^3.$

Congruence : Two shapes are called congruent if they have the same shape and size. Two integers are called congruent modulo $x$ if they have the same remainder in a division by $x.$

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

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.