**Interval notation is used to describe what numbers are included or excluded in a set.** When an arbitrary value x is greater than three but less than five, then in interval notation the set of values for x would be written as (3,5). In interval notation, parentheses denote exclusive inequalities.

Similarly, in interval notation, brackets are used to denote inclusive inequalities. As with the above example, if x is greater than or equal to three, and less than or equal to five, then in interval notation the set of values for x would be written as [3,5]. This means that x could equal any value from three up to five, including both endpoints. In the earlier example, x could not equal to endpoints of the set based on the inequalities given.