The angle (or pitch) of a rotor blade varies along its length (from hub to tip), i.e. it twists.
This can mean that the angle varies linearly, e.g. the rate of change is 0.1 degrees/cm along the whole length. Thus the degree of twist would be described using a single value (0.1, 100%).
The performance of a rotor blade, and hence a wind turbine, can be improved by varying the rate of change of this angle. So, e.g. it is 0.1 degrees/cm over part of the blade’s length (say 80%), but 0.05 (15%), and 0.15 (5%) over other parts of the length. Thus the twist would need a set of numbers to describe it; the twist distribution, [(0.05, 15%), (0.1, 80%, 0.15, 5%)].
I’m not sure that’s a very clear explanation, but I hope it helps.
These links might be useful; http://www.freepatentsonline.com/6497385.htmlhttp://www.aerodyndesign.com/ANALYSIS/ANALYSIS.htmhttp://aircraft-license.com/Demo/17.pdf
I'm afraid I have no idea how to describe this in German