In mathematics, an interval is a group of numbers that includes all numbers between the beginning and the end. Numbers that are larger than the beginning number and smaller than the end number are inside the interval, and numbers that are smaller than the beginning number or larger than the end number are not in the interval. The beginning number and end number may or may not be inside the interval. An example of an interval might be from 3.3 to 15. Here, numbers such as 4, 8, 9.5, 14, and even 14.999 are inside this interval. Numbers such as -4, 2, 3.2, 20, and 15.000001 are not inside this interval.