Often with mathematics, common words have different meanings which can be confusing. On top of that there is all the specialised vocabulary. This page aims to cover, in everyday language as well as more formally, all the mathematical vocabulary used.

When you see

it means continue the same pattern. For instance means .A pair of curly brackets/braces

is used to denote sets.The symbol

means approximately equal. says "the square root of 2 is approximately equal to one point four one."The symbol

means not equal to so means "p is not equal to 2".An overbar over part of a decimal means the digits repeat forever. For example

means that just the 6 is repeated giving , but means that the whole sequence is repeated: .The *absolute value* is the magnitude of , that is, the number with any negative sign removed. For example, and . Note that any calculation within the absolute value is done first and then the sign ignored eg .

A set is a collection of objects, for example,

is the set of numbers , and .The set with no elements, *empty set*, and has its own notation .

The objects in a set are called *elements*. For example, is an element in but is not. However, is an element of and is not since contains the elements , and .

If all the elements of one set are contained in another set, then the first set is a *subset* of the second set. (Formally, is a *subset* of is every element in is contained in .) For example, is a subset of . The empty set is a subset of all other sets as it has no elements.

Decimal numbers that do not go on forever are called *terminating decimals*. For example 0.3 is a terminating decimal but is not as the 3 is repeated forever. The decimal representation of is not terminating either. We might approximate it to a terminating decimal, but however many decimal places we use, it will never be exactly .

Decimals which do not terminate but repeat the same digit or sequence of digits over and over again are called *repeating decimals*. An overbar over the repeating digit or sequence of digits is used, for example, and .

When we want to express a decimal which does not terminate as terminating decimal, we *round* to a certain number of decimal places. For example , , and all rounded to 3 decimal places.

The *Positive Integers*, also called the *Natural Numbers*, are the numbers .

(Note that Natural Numbers sometimes include 0 so make sure you are always aware of which definition is being used in any books and webpages you're reading and in any courses you are taking.)

The *Negative Integers* is the set .

The *Non-negative Integers* is the set of positive integers and zero.

The *Integers* consists of the Positive Integers, Negative Integers and . That is, the Integers is the set .

The *real numbers* consist of all fractions, whole numbers and decimals. The numbers which are not real are called *imaginary numbers*. (To get the imaginary numbers we have to define the square root of -1 which we call *i*. Weird, huh?)

Rational numbers are numbers which can be written as a fraction where the numerator (top) and denominator (bottom) are both integers, and the denominator (bottom) is not 0. For example, 2/3 is a rational number since 2 and 3 are both integers, and

. Note that the integers are rational numbers since they can be written as a fraction with denominator (bottom) 1. In decimal form they are represented by either terminating or repeating decimals. For example, , and 0.Irrational numbers are real numbers which are not rational! They can not be written as a fraction with integer numerator (top) and denominator (bottom), and denominator (bottom) which is not zero. They can not be written as terminating decimals. They can not be written as repeating decimals. Examples of irrational numbers are *may* get a rational number eg .