A prime number is a whole number greater than 1 that can only be divided evenly by 1 and itself. This means it has no other divisors. For example, the numbers 2, 3, 5, and 7 are all prime because they cannot be divided by any other numbers without leaving a remainder. In contrast, numbers like 4, 6, and 8 are not prime because they can be divided by numbers other than 1 and themselves. Understanding prime numbers is important in various fields, including mathematics and cryptography, where they play a key role in securing information.