Tailslide's Air Combat Glossary

ACM  (Air Combat Maneuvers)
Various maneuvers that are flown when you are engaging the enemy.  Examples include the Split-S and Barrel Roll.
Barrel Roll
Similar to a roll, but you apply back pressure on the stick while you are rolling to the left or right.  This makes your plane fly in a corkscrew pattern and is often used to make the enemy overshoot.
BnZ (Boom n Zoom)  - See Energy Fighting
CC  (click click)
Clicking the microphone twice is a sign that you have heard a transmission.  The code 'CC' is typed in multiplayer games to indicate you have heard what your team mate is saying.  If you do not respond, your team mates must assume you have not seen their message and may repeat it..
Flying a plane in a large climbing spiral, staying at a fast speed.  It is a good way to drag slower enemy planes up higher without venturing too far away from your present location.
Energy Fighting
Fighting with the objective of keeping an energy advantage (speed / altitude) over your opponent.  Most useful in faster planes, but can be applied to any aircraft.  See this article on the P51 for a discussion of Energy Fighting.
To get separation (distance) from your opponent, usually with the purpose of gaining altitude and coming  back above them. Often used in Energy Fighting
Flat Scissors
Most fights degenerate into a flat scissors fight when both planes reach ground level.   The winner is usually the person with a better roll rate and turn rate.
Flat Scissors
Fig S1 - Flat Scissors
Ground Loop
Flipping the plane when it's on the ground,  can be caused by gusts of wind,   applying too much wheel brake, even revving the engine to hard on takeoff.
Gun Jam
Your guns may become jammed if you try to shoot in High G turns or if they become overheated.
Hammerhead Stall
This maneuver is performed by flying straight up, then just before your plane is about to stall you apply full rudder so the nose falls to the side and you point straight down again.  If an enemy chases you in a climb, this is a good way to get every last inch of altitude then reverse on him
High Yo-Yo
This is often used to prevent an overshoot. When you are chasing someone in a turn and you are catching up too fast, raise your nose above the horizon so you are climbing as you are turning.  This will trade your speed for altitude and ensure you stay behind the enemy.  The opposite of this maneuver is the low Yo-Yo.
Named after the WW I ace Max Immelman, this maneuver is the opposite of the Split-S.  You pull back until your plane is flying level and upside down, then you roll your plane right side up.  This is the most efficient was to gain altitude and reverse your direction.  Do not fly this when the enemy is anywhere near since it leaves you slow and vulnerable.
Low Yo-Yo
This is used to catch up to an opponent while turning, and to keep your speed up while turning.  If you notice you are getting slower and not catching up to someone in a turn, lower your nose below the horizon do you are descending while turning.  This has two effects - you keep your speed up and you can cut inside the opponents turn.
Out of Plane Turns
These are used for evading the enemy.  The concept is that you position your plane so your opponent must roll his plane to follow your turn. He will have no choice but to continue flying straight until he can roll his plane in the proper direction to pull back and give chase.
An overshoot occurs when you are chasing a plane from behind and inadvertently fly past him.  Maneuvers that are used to avoid an overshoot include the Barrel Roll, Snap Roll, High Yo-Yo and Immelman.  Maneuvers that are used to force your opponent to overshoot include cutting throttle, Barrel Roll, Split-S, and hard turns out of plane.
Rolling Scissors
See this article for a discussion of Horizontal Rolling Scissors.   There is another variation called a Vertical Rolling Scissors which is the same thing except spiraling down.
SA  (Situational Awareness)
As a pilot you must keep a mental note of all the planes in your area, and constantly be on the lookout for new threats.
Scissors - See Flat Scissors or Rolling Scissors
Snap Roll
A snap roll occurs when one wing of the plane stalls before the other.  This causes the plane to spin quickly around the wing that has not stalled (much more quickly than a normal roll).   The snap roll can be a useful evasive maneuver but it can put a lot of strain on the plane so you have to watch your speed and weapons load when you perform it.  Pull back the stick hard and rudder to the side you want to roll.  Not all simulators model snap rolls. 
Split-S  (Split Esse)
This maneuver is named since it looks like the bottom part of the letter S.  You roll your plane on it's back and pull back on the stick until you are flying level again.   This is a good evasive maneuver if someone is closing on you fast from above and you need to evade. The opposite of this maneuver is the Immelman.
Fly straight up, then when your plane runs out of speed it will actually slide backwards.  Soon after, the plane will violently flip around  (hopefully) nose down.
Wing Loading
Ratio of weight to wing area.  The lower the number generally the better the plane will turn and the it will be harder to stall.  High wing loading mean the plane will stall at higher speeds.
Climb steeply (but not straight up).  When your plane starts to slow, apply rudder until the plane is pointed back the way it came.  This is a good way to turn around when you are in a better climbing plane and you are done extending on an enemy.