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.

Boundary : The boundary of a 2-dimensional shape is the 1-dimensional shape that separates the 2-dimensional shape from the rest of the 2-dimensional space.

Center : The center of a circle is the unique point in the circle, such that all points on the boundary of the circle have a constant distance equal to the radius from that point. The center of a regular polygon is the point that has equal distance from all its corners.

Chord : A chord is any line segment between two points on the boundary of a circle.

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.

Circumference : The perimeter of a circle is called circumference. The length of the circumference $C$ can be calculated as $C=2\pi r=\pi d,$ where $r$ is the radius and $d$ the diameter of the circle. This means that the circumference of a circle with diameter 1 $cm$ (radius 0.5 $cm$) is about 3.14 $cm.$

Diameter : The diameter of a circle is the length of a line segment from the boundary of a circle through the center of the circle to the boundary on the other side of the circle.

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

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.

Radius : In a circle or sphere the radius is the distance between the center and the boundary.

Least common multiple : The least common multiple of two numbers is a number that is a multiple of both numbers such that there is no smaller number that is also a multiple of both numbers. For example the least common multiple of 4 and 6 is 12.

Multiple : A multiple of a number $x$ is any of the numbers $1x,2x,3x,4x,\ldots.$ For example the multiples of 7 include 7, 14, 21 and 70.

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