An even number is any integer (a whole number) that can be divided by 2. If you can cleanly divide a number by 2, the number is even. If you divide by 2 and there is a remainder left, then the number is odd.
Let's try that calculation...
102 ÷ 2 = 51
Notice the answer is a whole number and doesn't have a remainder? That means the number is even, as it can cleanly be divided by 2, with no remaining remainder.
Any number that ends in 2, 4, 6 or 8 is even. If the number is larger than 10, if it ends in 0 it is also an even number. They are even because they can be divided by 2 evenly.
Here are more examples of even and odd numbers in sequence: