fifth wheel

The phrase "fifth wheel" typically refers to someone who is an extra or unnecessary person in a social situation or group. This term is often used to describe a person who feels left out or awkward because they do not fit into the established dynamic or have a specific role or purpose in a particular group or activity. The origin of this phrase can be traced back to the fifth wheel attachment, which was an extra wheel added to carriages or wagons for stability, but was not necessary in all situations.