This list is not exhaustive but it gives you an insight into some of terms used in rocketry

Airframe The rocket structure. This usually refers to just the cylindrical body tube, but may also refer to the entire body of the rocket.

Ammonium Perchlorate (A.P.) Composite (mid- and high-power solid fuel) motors is generally made with ammonium perchlorate as the oxidizer and various other ingredients as the fuel.

Altimeter is a device, which measures at least the maximum height a rocket reaches. These are often combined with circuitry to separate the rocket at apogee for recovery.

Apogee is the highest point of a rocket flight. An ideal rocket flight opens the rocket and ejects the recovery system at apogee.

Black Powder (B.P.) is used for ejection charges on some rockets when it is unfeasible for motor-based ejection charges to be used, it is also the propellant used on small Estes and Quest Model rocket motors.

CATO means that a motor blows up! This is rare for production pre-manufactured motors but it can happen.

Centre of Gravity (C.G.) is the balance point of the rocket with the intended motor loaded. You can measure the C.G. directly on a finished rocket by installing the motor and finding where it balances on an edge (like a see-saw).

Centre of Pressure (C.P.) is the balance point of aerodynamic forces on the rocket. You can calculate the C.P. using various rocket simulation programs. If the C.P. is not well aft of the C.G., the rocket will not be stable.

Certification The United Kingdom Rocketry Association’s method of assessing a persons ability, and have shown they can build a rocket, fly it safely and recovery it without damage at up to three levels.

Cluster When two or more motors are used to power a rocket it is referred to as a cluster.

Ejection charge (or sometimes mechanical system), which opens the rocket at apogee to deploy the recovery system. 

Ejection delay is the amount of time between motor burnout and the deployment and it timed to occur at apogee.

Fins (you knew this one) are the flat parts, which stick out from the tube at the aft end of the rocket and provide stable flight. Without fins (or other special arrangements), the rocket will not fly in a straight line.

HPR High-power Rocketry

Ignition Solid-fuel motors are ignited electrically using an "ignition system." An "igniter" is inserted into the motor and when electricity is passed through it, it bursts into flame, igniting the motor. This allows the motors to be launched with everyone at a safe distance.

Impulse is the measure of thrust over time (in Newton-seconds or pound-seconds of force). The "total impulse" of a motor is the amount of energy it provides to lift the rocket and the source of the letter designation ("A, B, C" and so on).

Launcher A launcher is required to hold the rocket in a vertical position and guide it straight during the beginning of its flight (before the rocket gains enough airspeed for the fins to take effect). The most common kind of launcher is a base with a thin steel rod to which the rocket attaches with a "launch lug."

Level 1 is the first step in the UKRA Certification assessments and refers to rockets, which use H, & I class motors.

Level 2 is the second step in the UKRA Certification assessments and refers to rockets, which use J, K & L class motors.

Level 3 is the third step in the UKRA Certification assessments and refers to rockets, which use M class motors, and above.

Motor The motive force making a rocket go. Solid fuel rockets use motors because there are no mechanical moving parts (they're not engines).

Nose The forward end of a rocket. The tapering (pointy) part of the rocket is often referred to as a "nose cone," even though the shape is rarely conical.

Recovery Rockets must be recovery safely. If a rocket comes down without a recovery system, it will fall nose down very fast and will be dangerous. Getting your rocket back in once piece is important as part of a successful flight (not to mention that it allows you to fly again). The most common recovery systems are parachutes and streamers although many others have been devised.

RMS stands for Reloadable Motor System. The propellant is contained within a reusable aluminium casing. The user must assemble the motor & reload before use.

Parachute ('chute) The most common rocket recovery system and the only one used with larger rockets. Model rocket often use flat plastic "Para sheets" which are attached to the rocket with thread. Larger rockets use true parachutes because of the weight being recovered.

Shred When a rocket breaks up in flight, it's called a "shred." Rockets shred because they aren't stable, too large a motor is used for the materials, or they have not been properly constructed.

Separation When the recovery system comes out too early or too late and the rocket is still moving too fast, the recovery system takes a strong jerk. If it breaks, the two parts become detached and you have a separation.

Streamer A recovery system for the smallest of model rockets. Streamers are flat plastic, paper or cloth bands, which are attached to the rocket and flap as the rocket comes down, slowing the descent.

Thrust is a measure of instantaneous force (in Newton’s or pound of force). The "average thrust" of a motor is the average amount it pushes on the rocket during it's entire burn phase. Note that the motor generally produces different amounts of thrust as it burns and a graph of this is called a "thrust curve."

Zipper this is when the ejection charge goes off too soon, this results in the airframe separating and the parachute deploying while the rocket is travelling at speed, then the recovery harness rips through the airframe causing the zipper.