A set is a collection of elements (usually numbers)

E.g. {$x \in R | x$ > 0} should be read as "the set of all x's that are an element of the real numbers such that x is greater than 0."

Special symbols:

- $R$ = real numbers

- $Z$ = integers

- $N$ = natural numbers

- $Q$ = rational numbers

- $C$ = complex numbers

- $I$ = imaginary numbers