0 Do a Barrel Roll

         The barrel roll is so named because an aircraft executing this maneuver looks as though it were flying with its wheels running along the inside edge of a barrel. A more common modern visualization is to imagine an airplane trying to fly in a horizontal corkscrew around the line of the direction of travel.
“Do A Barrel Roll” is a catchphrase used to call on someone to perform a 360 degree horizontal spin. The phrase is sometimes used to caption image macros where the subject appears to be in mid-rotation, or in animated GIFs where the subject is performing a full rotation.
The barrel roll has been used as an airplane aerial combat technique since dogfighting emerged in 1913 during World War I. The barrel roll maneuver was later included as a move in the Super Nintendo console game Star Fox that was released in the US the spring of 1993. In the game, the player could perform a barrel roll by double tapping the L and R buttons, protecting the ship from enemy lasers. The phrase “do a barrel roll” comes from the sequel Star Fox 64 released on July 1st, 1997, in which the character Peppy Hare orders you to “Do a barrel roll!” while approaching 4 stationary turrets firing lasers.
The first Urban Dictionary definition was created on January 30th, 2004. During the Tom Green raids of 2006, the phrase was often used to prank call Green during his show. It is often quoted on the image board 4chan and one of the earliest archived threads dates back to August 2nd, 2007. A Facebook. fan page has 14,796 likes, and there are 218 YTMND. submissions as of November 3rd, 2011. The phrase has spawned an image macro fad on the site I Can Has Cheezburger.
In aviation, the maneuver includes a constant variation of attitude in all three axes, and at the midpoint (top) of the roll, the aircraft is flying inverted, with the nose pointing at a moderate angle to the general path of flight. The term "barrel roll" is frequently used, incorrectly, to refer to any roll by an airplane (see aileron roll). Most often, a barrel roll refers to a helical roll around the relative forward motion of the aircraft, in which the nose ends up pointed along the flight path. It is performed by doing a combination of a roll and a loop.
Outside of aerobatic competition, the Boeing 367-80 and Concorde prototype were barrel rolled during testing. The Boeing 367-80 was rolled twice by Tex Johnston in an unauthorized maneuver while demonstrating the aircraft to the International Air Transport Association over Lake Washington, Seattle. The Concorde was rolled multiple times by her test pilots, including Jean Franchi and Brian Walpole.
To do a barrel roll from the pilot's perspective, it may best be thought of as a roll around a point on the horizon that is 45 degrees off the flightpath. Starting from a level flight, the pilot will usually pick such a point on the horizon as a reference. The pilot will then pull back on the stick, bringing the plane up into a brief climb. As the nose passes through the horizon, the pilot begins to apply aileron input, which is accomplished by easing the stick to either the right or the left. As the airplane rolls it will continue to pitch upward. The pilot will need to control the roll rate, keeping the nose 45 degrees off the reference point on the horizon as the plane rolls around this spot. Some planes may require rudder input, while most high powered planes will only need to be guided by aileron and elevator control.
When the aircraft has rolled 90 degrees, and the wings are vertical, the nose should be pitched about 45 degrees directly above the reference point on the horizon. As the plane continues to roll upside-down it will begin to level out, and the horizon will appear to rise to meet the nose. When in the completely inverted position, the aircraft should be level and the nose should still be 45 degrees to the side of the reference point, putting it 90 degrees off of the original flightpath. As the nose drops through the horizon, the pilot may need to reduce the elevator pressure, to counter-act the force of gravity and the loss of lift. Still keeping the nose 45 degrees off the reference point, the plane should roll into level flight along the same flightpath and at the same altitude at which the maneuver began.
 In air combat maneuvering, historically known as dogfighting, a barrel roll may refer to one of many maneuvers. These maneuvers are often simply called barrel rolls, but many fall into the category of "displacement rolls."
The term barrel roll, by itself, most often refers to a helical roll around a straight flight path, the purpose of which is to slow the relative forward motion of the aircraft. This can help a defender to force an attacker, who is usually behind the defender, to fly out in front, called overshooting. This can also help an attacker to prevent an overshoot. This often forces both planes to continue through a series of rolls known as a rolling scissors maneuver. A barrel roll is also often used to check blind spots while remaining on a steady flight path.
The rolling scissors, also called vertical scissors or simply "rollers," is usually an undesirable maneuver to be caught in, both for the attacker and the defender. The advantage usually goes to the aircraft with the higher turn rate, especially when pulling the nose through the top and bottom of the turns. Correct placement of the lift vector during the maneuver is crucial to keep from moving ahead, relative to the opponent. There are many optical illusions that affect the pilot's ability to determine the relative position of the opponent, and mistakes can easily be made. It is extremely difficult to get a suitable firing solution during the rolling scissors. If the aircraft have a thrust-to-weight ratio of less than one, each consecutive roll will be lower than the previous, and the pilots can quickly find themselves at ground level. Any advantage is usually lost by the first pilot that attempts to disengage.
A high g barrel roll is a last ditch defensive maneuver, performed when the attacker has achieved a suitable firing solution. The maneuver is performed when the attacker is very close, and a barrel roll performed by the defender may cause an overshoot. The maneuver begins by cutting the throttle, extending the speed brakes, or turning very hard to encourage an overshoot. The maneuver is then executed by applying hard rudder input during the barrel roll to assist with the roll. The sudden change in the relative forward speed may cause a surprised attacker to fly out in front of the defender. Depending on the situation, a high g barrel roll can be performed "over the top," by beginning the roll like a normal barrel roll. The roll can also be performed "underneath," by doing a half aileron roll into the inverted position and beginning the barrel roll while upside-down.
A barrel roll attack is a military maneuver that improves the attacker's offensive position and prevents the attacker from overshooting. In this maneuver the defender breaks one direction and so the attacker performs a barrel roll in the opposite direction. The attacker pulls back on the stick more than a normal barrel roll, performing a tighter loop than the roll. It is the three dimensional equivalent of a 90 degree turn, and the attacker finishes the loop, having completed three quarters of a roll, with the nose pointed along the defender's flight path^.
The maneuver is performed when an overshoot is imminent and cannot be corrected with a normal displacement roll. Much more aggressive than a normal displacement roll, the maneuver begins by rolling slightly toward the direction of the defender's break, and then pulling up sharply. At roughly 30 degrees from the horizon, the pilot begins the barrel roll away from the defender's break, applying more elevator pressure than roll. When inverted, the pilot then uses the assistance provided by gravity combined with rudder control to bring the fuselages of both aircraft into alignment. As the nose passes through the horizon, the pilot will then align the lift vector ahead of the defender, to bring the fighter back into the correct geometric plane, inside of the defender's turn.
The success of a barrel roll attack depends greatly on the aircraft's ability to zoom climb. As the attacker is coming down, the defender may counter by pulling up unto a barrel roll, resulting in a rolling scissors.

Notable Examples

Source : "http://en.wikipedia.org/wiki/Barrel_roll" and "http://knowyourmeme.com/memes/do-a-barrel-roll"