If the HCF of two numbers is 1, the numbers are called co-prime numbers.
Explanation:
If the HCF of two numbers is 1 that means there is no common factor except 1. Those types of numbers are called co-primes.
For example: (2,3), (3,5), (8,15), (10,33) etc
For the HCF to be 1, they themselves need not always be prime numbers, like for example (6,35) are coprime. Both 6 and 35 are composite numbers.
Therefore, If the HCF of two numbers is 1, the numbers are called co-prime numbers.