A composite number is a number that's not prime. A prime number is a number who only has 2 factors (1 and itself). A composite number has multiple factors.
For example; 7 is prime, as the factors of 7 are only 1&7. 14 is composite, as there are 4 factors (more than 2); 1&14, 2&7.
91 is composite, as it has the following factor pairs; 1&91, 7&13.
139 only has 1&19, making it prime. 13 only has 1&13, making it prime. 29 only has 1&13, making it prime.