An odd number is a whole number that is NOT divisible by two.

An odd number is a number that has 1, 3, 5, 7, or 9 in the ones place.

1, 3, 5, 7, 9, 11, 13, 15, 17, ...

Any odd numbered group of items can't be divided into two equal groups of items. When an odd numbered group of items is divided into two groups, one item will always be left over.