An integer is a whole number. Fractions and decimals are not included in this set. They are sometimes also called natural numbers and consist of the numbers that you can count, starting at zero, and their negative counterparts for example 2, 6, -89; are all integers, while 2.4, 66.7 are not integers. To answer the question of what is the smallest integer, it is negative infinity; there is no smallest integer because there will always be one number lesser.