**absolute value:** the distance of a number from 0 and is always positive. It is presented by vertical lines, such as |-4|, which is representative of ‘4’. Distance can only be either positive or 0, and never a negative number.

**algebra:** branch of mathematics that substitutes letters and symbols in place of numerical values, to create operations, equations, and expressions.

**algebraic expression:** expression that contains a minimum of one variable, e.g. X^{2} - 5

**congruent:** identical in terms of size and shape, as well as all relevant aspects.