What do we call numbers you can split into two equal groups?

Even numbers are what we call numbers that can be split into two equal groups with nothing left over, like counting by twos: 2, 4, 6, 8. If you take four toys, you can split them into two groups of two exactly, and that even split is what makes a number even.

Odd numbers are the opposite, they always leave one item left over when you try to split them into two equal groups, like trying to share five cookies evenly between two people. Big numbers isn't a real category describing this splitting property at all, it just refers to size, not whether a number splits evenly.

You can tell whether any number is even or odd just by looking at its very last digit, numbers ending in 0, 2, 4, 6, or 8 are always even, no matter how enormous the rest of the number is.