One who deters the socialization of a couple, perhaps when being invited out of pitty or through a feeling of duty. This person may be eased into the situation by being allowed to stay in an envirnment he or she has become accustomed to (perhaps a kitchen, where the third wheel can bake cookies for the couple.) The third wheel may feel uncomfortable about watching the couple canoodle on his her her sofa, but none of this is taken into consideration.

A person hanging out with two people (usually a couple) that are in a sence leaving him/her out. Called the third wheel because either:

-Having any odd number of wheels on an object generally messes it up.

-Third wheel on a bike makes a tricycle, something thats safe for kids be left alone with.

To be the friend that sits there while your friend gets pussy and you get nothin but yourself.

The odd one out. The person who always gets slobbered on while he/she watches their friends canoodle.

When in a group of three there is always the one that doesnt fit in. We consitter him/her as the "3rd wheel" because they just dont fit. If there is a couple together and then one of there cousins, it just doesnt make since for the cousin to be there. If there are two caucasian people standing with a black man, the black man is obvously the "3rd wheel". Two Catholics and a Jew, Two Canadians and a Mexican, and so on