A prime number p is only divisible by itself and 1. It has no other divisors. If we include negative numbers in our world, p is divisible by ±p and ±1, and nothing else. The numbers 1 and -1 are usually not considered prime. They are called units, a term that is used in more general settings. Zero is also not prime, as it is divisible by everything.
A number, other than 0 or ±1, is called composite if it is not prime. It is "composed" of other numbers. Note that prime comes from an old latin word meaning first. Primes are the first numbers, and they are multiplied together to build composites.