I'll take a few (and correct one along the way). Some of my answers may be more RC shorthand than absoltuly technically correct.

Powerloading - the amount of power compared to the weight of the airplane. The same as power-to-weight ratios, though in different units. High power loading means lots of engine power available compared to the weight of the plane.

Chord - distance "front to back" of a wing.

MAC - Mean Aerodynamic Chord - The average chord of the wing. On a straight wing, it's the same as the chord. On a tapered and/or swept wing, you have to figure it out by averaging the tip and root chords. Often you also want to average the location of the MAC compared to the root, or fuse, as CG (center of gravity) is figured in terms of the MAC. (ie, 25% of MAC)

Chord Thickness - I'm not 100% sure on this one. I THINK they are talking about the thickness of the airfoil, usually expressed as a percentage of wing chord. So a particlar airfoil would be, maybe 12% thick. That means that the thickest part of the airfoil is 12% of the wing chord, so a 10in chord wing would be 1.2in thick.

Camber - The amount of curve of the center line of the airfoil. Take an airfoil picture, and measure a point exactly half way between the top and bottom surface of the airfoil. and do this all the way from the LE to the TE,and you get a line. Any curve in this line is Camber. A symetrical airfoil has a perfectly straight center line, and thus has 0 camber.

The term "under-cambered" referring to an airfoil means the bottom surface of the wing is concave, but it's actually a kind of mis-nomer and shouldn't be confused with the airfoils actual camber. Usually an airfoil is spec'd by it's max camber, ie, the farthest from a straight line that the camber line gets. Any unber-camber effect that results is really just a side effect of the camber and the thickness of the wing.

Leading Edge Strake - The big that sticks out from the LE near the root on planes like the F/A-18, making the wing root look really large compared to the rest of the wing. (I think I got that one right)

Pitching Moment - When an airfoil generates lift, it also creates a tendancy for the wing to twist. If you've ever seen a wing fall off a plane in flight, you've seen that the wing will spin, usually moving the LE upwards. That's the pitching moment in effect with nothing to counter it. Different airfoils have a larger or smaller one. The larger the pitching moment, the harder the horizontal tail has to work.

Incidence - Angle of (usually) an airfoil (wing, tail, whatever) to a reference line (usually a line on the fuse that should be level in level flight, or a line that is convenient to the design, such as a fuse center line, but any arbitrary line will work). The airfoil is measured on a line drawn from LE to TE. (A flat plate, such as a sheet stab is still an "airfoil")

Winglets - As mentioned, they are the little thingies sticking up (or down, or both) on the wingtips. They mess with the tip vortex that is formed by the wing, as air trys to go around the wingtip from the bottom of the wing to the top. (which forms the wing tip vortex). The winglets have several effects, depending on the plane in question. On a swept wing, espcially a flying wing, they serve as extra vertical stab area and help with yaw stability. They can also help the wing generate more lift for the given wingspan. They can also help a tip-stalling tendancy. I also use them to reduce aileron flutter, as it smooths out the tip vortex in the area the ailerons operate.