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

Subtraction : Subtraction is the mathematical operation that describes decreasing a number by an amount equal to a second number. The mathematical symbol for subtraction is the minus sign $-.$ The term subtraction is also used for a generalization of this basic operation on numbers to functions, vectors and matrices.

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.

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.

Rectangle : A rectangle is a quadrilateral with 4 right angles. Two opposing sides in a rectangle have the same length. They are sometimes referred to as the width and the length of the rectangle. To calculate the area of an rectangle one can multiply the width of the rectangle by the length of the rectangle. A square is the special case of a rectangle in which all side lengths are the same. Every rectangle is a parallelogram.

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

Sphere : A sphere is a three-dimensional shape that has a boundary equal to a set of points with a constant distance to a point. The point is called the center of the sphere and the distance is called the radius $r$ of the sphere. The volume of a sphere with radius $r$ is $\frac{4}{3}\pi r^3$ and the surface area is $4\pi r^2.$

Triangle : A triangle is a polygon with three corners and three sides. You can calculate the area of a triangle by multiplying half the length of the base by the height on that base. The sum of the interior angles in a triangle is always $180^{\circ}.$

Kilogram : A kilogram or kg is a unit for weight equal to 1,000 grams.

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

Measurement : To measure something or to get a measurement is to quantify a physical attribute given a choice of unit using the appropriate tool for measuring that specific physical attribute (for example a scale for weight or a measuring tape for length).

Pound : A pound or $lb$ is a unit for measuring weight. One pound equals 16 ounces or approximately 454 grams.

Scale : Scale refers to the size of a shape. A scale drawing changes a shape to a similar shape of a different size.

Unit : When measuring an attribute a particular unit specifies which size of the specific attribute is represented by the number 1. For example 1 $cm$ equals 10 $mm$, so when changing the unit we will also have to change the quantity to still represent the same measurement.

Weight : Weight refers to the property of objects that can be measured with a scale.