Short for Plebeian.
Today, Pleb is often used to describe a person who appears to belong to the lower or middle classes of society.
This term was originally used to refer to the class of common people in ancient Rome. These people were often poor or middle class, but could also be very wealthy. A wealthy Pleb differed from a Patrician (the elite/upper class) because they were not born into their social status, but rather moved up in society on their own steam.
Upperclassman: "He doesn't have an education and he has a crappy job that earns him very little money. He's such a Pleb"
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