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.

Line segment : A line segment AB is a one-dimensional shape consisting of the points A and B and all the points on the straight connection of A and B. A and B are both endpoints of the line segment AB.

Pyramid : A pyramid is a polyhedron that has a base equal to a polygon. In addition to the corners in the polygon the pyramid has exactly one additional corner, the so called apex of the pyramid. All the corners of the base shape are connected to the apex and all the faces besides the base face are triangles.

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 $360^{\circ}.$

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

Three-dimensional shape : A three-dimensional shape is a shape that has a volume.

Volume : Volume refers to the size of a three-dimensional objects measured by how many unit cubes it would take to fill the shape.

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.

Distributive property : The distributive property is defined by $a(x+y)=ax+ay$ for all $a,x,y.$ The distributive property is implicitly used whenever one multiplies out brackets or uses standard algorithms for multiplication or division.

Equation : An equation is a mathematical statement in which two expressions are written with an equal sign in between. A solution of an equation is a set of variables that makes the statement a true statement.

Solution : A solution to an equation is a choice of variables that when substituted into the equation results in a true statement.