A **set** is any collection of items. In mathematics, a set is represented using a capital letter and curly brackets. For example, if *S* is the set of all integers less than 10, then *S* = {*x*|*x* is an integer and *x *< 10}. (The vertical bar | is read “such that.”)

The set that contains no elements is called the **empty set **or the** null set** and is denoted by empty brackets { } or the symbol ∅.

The **union** of two sets, denoted *A* ∪ *B*, contains all the data that is in either set *A* *or* set *B* or both sets. The **intersection **of two sets, denoted *A* ∩ *B*, includes only elements that are in both *A* *and* *B*.