Aerofoil: cross section of a wing or blade designed to produce lift or a force when in an airflow.

It is commonly designed with a convex curve on the top and a straight or slightly concave curve on the bottom. The front or nose is usually well rounded with a sharp trailing edge.

Airspeed: the speed of an aircraft through the air, and is not necessarily equivalent to the ground speed.

e.g. if the aircraft speed is 130kts (Kts) with a tail wind of 20 kts then its ground speed will be 130+20=150 Kts. If the aircraft were to turnaround and fly into the wind (head wind) then its ground speed will be 130-20=110kts.

Note: this is the reason why aircraft always land into the wind or head wind to lower the speed. Aircraft also take off into the wind to reduce the speed.

Knot: 1 nautical mile per hour which is equal to 1.15 statute mile, 1kt=1.15 mph

Fluid: liquid or gas and sometimes powders which acts as a fluid. In other words, a substance that will flow.

Incompressible flow: for flow below sonic speed, the fluid is assumed to be incompressible although this is not 100% applicable, it is still averagely correct (speed of sound 762mph at sea level). At supersonic speed, air is compressible. When an aircraft flies at a speed approaching the speed of sound, shock waves cause a large increase in drag. At the beginning of the transonic speed, an increase in drag starts and some parts of the air around the aircraft behaves as if it is compressible.

Laminar flow fluid: flow in which streamline maintain a uniform parallel separation without turbulence. This is considered a good condition which reduces drag.