Bumping can be good or it can be be bad. Airline bumping is what happens when a passenger is holding a confirmed ticket for a flight (meaning you've purchased a ticket and you've checked in for the flight, either at the gate or up at the check in desks) and the airline doesn't let you board. Instead, they provide travel on a future flight to the same city, and some type of compensation (usually a voucher for future travel or a free ticket). If you don't want to get bumped (perhaps you have an important business meeting that day, consider these tips from About.com's Guide to Airline Travel on how NOT to get bumped.
Types of Bumping
Bumping can happen voluntarily or involuntarily. In voluntary bumping, a passenger may see that the flight is full or overbooked and ask to be bumped or to have his or her name put on the bumping list. If a passenger is voluntarily bumped, the airline will typically be offering a voucher for a predefined amount, such as $300, plus a seat on the next flight.
But bumping also happens involuntarily. That's when the airline denies you boarding, even if you have a confirmed seat. This also only happens in oversold situations, but it happens when no passenger volunteers to give up their seat.
For more information on specific bumping practices, ask the airline you're flying on for their rules and compensation policies for bumping. For more information on what to ask for in a voucher if you are bumped, consult About.com's Guide to Air Travel's tips for negotiating being bumped.
How to Get Bumped
Personally, I've had both good and bad experiences with bumping. A number of times, when I've had the time to wait and wasn't in a rush to get somewhere, I've volunteered to give up my seat to earn a free future ticket or voucher for future travel. If this is what you're hoping to do, you usually want to get to the gate early and have your name put on a bumping list by letting the gate agent know you'd be willing to take a later flight. Of course, be careful and check when the next flights might be, and if the airline will put you up overnight if the next flight is the next day.
Business travelers looking for the best fare, may want to consult our list of the best ways to get the best air fares.