This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
Airfoil: Cross section shape of the wing surface. Glider wings
are rarely symmetrical, and for our models are mostly flat
Angle of Attack (AOA): The angle of the mean chord line with
respect to the airflow, with zero AOA being defined as the
zero lift angle of the wing. More simply, it's the angle the
wing hits the air.
Angle of Incidence: The angle between the wing and the thrust
Aspect ratio: The ratio of wing span to wing chord. AR =
span^2 / area Higher numbers tend to be more efficient, but
can be weaker.
Canard: A glider with the stab in front of the wing. These
usually have very good stall characteristics. They appear to
be built "backwards".
Chord: The maximum front to back length of the wing, usually
the root where it is attached to the fuselage. Also used Root
chord, Tip chord.
Decalage: The amount of angle that the stabilizer is tilted
from the angle of the wing. This angle is usually slightly
negative, either leading edge down or trailing edge up. Used
to give a very slight up elevator pitch to the glider and help
it recover from dives.
Dihedral: The amount the wingtips are raised from the wing
root. Used to keep the model roll stable in glide. A typical
free flight model will have about 15 degrees of dihedral, or
about 1" for each 8" of span. Trihedral is when you have three
wing sections, the center section being horizontal.
Polyhedral is when you have four or more wing sections at
different angles. Anhedral is when the tips are pointed down,
occasionally found on the stab.
Dive: When the nose of the glide drops in flight.
Fuselage: The glider body, usually a stick.
Incidence: see Decalage.
Laminar: smooth air flow over a wing with no disturbances. Not
Lift: Upward force created by airflow as it passes over the wing.
Neutral Point: Is the glider CP.
Pitch: The rotational axis where the nose moves up or down. If
you make a "gun" with your hand, then extend your middle
finger straight out, you have the three axis of a glider. The
middle finger is the pitch axis. The index finger is the roll
axis. And the thumb is the yaw axis.
Reynolds number: A dimensionless number which describes the
type of airflow over a wing, also used to scale wings for wind
tunnel testing. The formula for it is:
Re=density(air)*velocity*length(chord)/viscosity(air). Re for
our models typically are under a million and are considered
the very low Reynolds number region.
Roll: The rotational axis where the glider leans towards one
side or the other.
Span: The distance from one wing tip to the other.
Stabilizer (stab): the horizontal part of the tail.
Stall: When a wing suddenly loses lift. When this happens, the
glider will first nose up, then the nose will rapidly drop and
Sweep: The amount the leading edge of the wing angles back
from the wing root. Sometimes the sweep will be negative, and
the tip is actually swept forward.
Tail spin: An antiquated term for what we refer to now as a
"spiral dive". It is not related to a stall or spin in any
way. When this model suffers a problem, it typically is a
spiral dive, which can result from grossly unequal angles of
incidence between the tip sections on either side, or excess
noseweight, or both. (RobEdmonds)
Washin: The amount the wing trailing edge is bent down. This
increases the lift of this portion of the wing.
Washout: The amount the wing trailing edge is bent up,
relative to the leading edge. Not dihedral, but actual
fore/aft warpage, usually to keep whole wing from stalling at
once. This decreased the lift of this portion of the wing.
Wing Loading: Ratio of wing area to glider weight.
Xerclod: The name given by the MITrs to the pod hook referred
to by Stine as "piece X".
Yaw: The rotational axis where the glider turns left or right.