Original: Thus Theorem 1 of takes the form, "Every positive integer, except 1, is a product of one or more primes," and Theorem 2 (their "Fundamental") asserts uniqueness. By convention, the number 1 is not itself prime, but since it is the product of no numbers, it is often convenient to include it in the theorem by the empty product rule.
Simplified: The theorem says that every positive integer greater than 1 can be written as a product of prime numbers (or the integer is itself a prime number).