Definition

A loud, enthusiastic greeting popularized in New York and New Jersey where the person being greeted is obligated to yell it back even louder—basically a verbal arms race of friendliness.

Example Usage

"When I saw my boy on the street corner, I yelled 'YERRR!' and he screamed back 'YERRRRRRR!' so loud people turned around."

Source: Urban Dictionary (https://www.urbandictionary.com/define.php?term=YERRR&defid=13101454)