Lay line: an imaginary line on which you can sail directly to your target without tacking.
Leader Lines: Short thicker lines from the control bar to the flying lines. Used to keep the pilots fingers away from the flying lines.
Leading edge, LE: the windward side of the kite, (the forward side that the wind hits first). This is the big inflatable tube on an inflatable kite. Or the side that has the opening for the cells on a foil kite.
Lift: when flying, a kite generates lift or upward force like an airplane wing. Lift is proportional to the square of the apparent wind velocity.
Lift-to-drag ratio, L/D, LDR: a measure of the efficiency of a kite. High L/D means the kite has a high top speed and flies at a greater angle to the wind, which results most noticeably in better possible VMG to windward and faster possible board speeds. Kites are not as efficient as sails, their L/D rarely exceeds 4.0 while a good yacht sail manages 10 and sailplanes (gliders) get over 50.
Lit: The period or act of being hooked up to a very powered kite.
Leech Line: a line that runs inside the trailing edge of the kite to prevents vibration and noise.
Leeward: the direction away from the wind. Opposite of windward.
Lift: upward pressure which the wind exerts on a kite.
Line Set (lines): the strings which are used to control the kite.
Locked in: also called being "parked": sailing along with the kite is remaining stationary in the sky relative to the rider - not moving the kite around but just letting it fly straight in the direction of travel.
Luff: When a kite folds or falls from the sky. A kite luffs when the air flow stalls. It may then stall and fall out of the sky. Luffing will occur if the kite gets too far upwind. Luffing may occur whenever there is a loss of tension on the lines.