What is the origin of the idiom "the odd one out" and when to use it?

The idiom "the odd one out" originates from the concept of identifying a person or thing that is different or does not belong in a given group or set. The phrase is typically employed when there is a clear contrast or anomaly within a group, highlighting the uniqueness or peculiarity of the individual or item in question. This idiom is often used to emphasize a sense of being different, separate, or out of place.