see e.g. (compare the mathematical expressions for the Weibull distribution in the original documents):

http://www.weibull.com/hotwire/issue14/relbasics14.htm
An important aspect of the Weibull distribution is how the values of the shape parameter, b, and the scale parameter, h, affect such distribution characteristics as the shape of the pdf curve, the reliability and the failure rate.
[...]
The Weibull shape parameter, b, is also known as the Weibull slope. This is because the value of b is equal to the slope of the line in a probability plot. Different values of the shape parameter can have marked effects on the behavior of the distribution.

www.rz.rwth-aachen.de/mata/ downloads/statistik/KapI_5_2seiten.pdf
Weibull - Verteilung:
Beschreibung des Ausfallverhaltens von Geräten, Baugruppen etc.
[…]
a: Maßstabsparameter
(Charakteristische Lebensdauer)
b: Formparameter
(Ausfallsteilheit)
c: Lageparameter
(Ausfallfreie Zeit; c=0: zweiparametrige
Weibullverteilung)