Being denied boarding, otherwise known as "bumping," happens when airlines oversell a flight. If you're involuntarily bumped from an oversold flight, you may be entitled to compensation.
Can you get bumped from an overbooked flight?
You get bumped involuntarily from an overbooked flight."The flight's full." Here's how to make the best of the situation. Know your rights. The U.S. Department of Transportation has established some rules for airlines to follow when bumping passengers from an overbooked flight.
What happens if a flight is oversold and nobody volunteers?
Sometimes, when an airline asks for volunteers to give up their seats and fly on a different flight, there are not enough volunteers. When this occurs, the airline will select passengers to give up their seats. This is called “involuntary denied boarding” or “bumping.”