In mathematics, the capital symbol z is used to represent the set of all integers, including positive integers, 0 and negative integers. All integers form an integer set, which is a number ring. In the integer system, zero and positive integers are collectively called natural numbers. -1, -2, -3, -n, (n is a non-zero natural number) are negative integers. Positive integers, zero integers and negative integers form an integer system. Integers exclude decimals and fractions.

So -7 belongs to integer set z.