Karen is an internet slang term for a bitchy, rich or middle-class, white woman who complains about everything and acts like she is the biggest victim in the world.
Examples: A black man who works for the park asked a Karen to please put her dog back on its leash while it was in the rambles of NY Central Park. She called the cops on him and tried to get the cops to kill him.
A Karen called the cops on a black 8-year-old girl for selling lemonade in her front yard, without a permit.
A Karen called the cops on a black family BBQing at a public park using the brick oven that she had planned on using but they got there first.
A Karen called the cops on a black nurse who was sitting on a bench in a public park, near where she lived because she was sure "that woman did not live in her building". (Spoiler: She did)
See a pattern? We do.
People noticed they also almost always had a variation of the same exact hair-style so it became a meme.