1, definition: odd number refers to a number that is not divisible by 2, which is also commonly known as singular number. Even number refers to a number divisible by 2, which is also commonly known as even number.

2. Relationship: Integers can be divided into odd numbers and even numbers. Numbers that are divisible by 2 are called even numbers, and numbers that are not divisible by 2 are called odd numbers. Even numbers can usually be represented by 2k (k is an integer), and odd numbers can be represented by 2k+ 1 (k is an integer). Please note that 0 is an even number, because it is divisible by 2.