To use your example:
EF-S 17-85 f/4-5.6 USM IS
EF-S = Canon EF mount variation with reduced image circle size, specifically for 1.6-crop DSLRs. Fits only newer entry-level DSLR cameras, currently 300D, 350D, & 20D.
17-85 = Zoom lens with a range of focal lengths from 17mm (wide angle) to 85mm (moderate telephoto)
f/4-5.6 = Range of maximum aperture, from f/4 at 17mm to f/5.6 at 85mm
USM = Ultrasonic Motor focusing. THere are two types, ring motor and micro-motor. Both are labeled USM, ring motor is the most modern.
IS = Image stabilization. Canon's system for reducing effects of camera shake.
EF 14mm F/2.8 USM L
EF = EF mount, will work with any EOS system camera
14mm = fized focal length of 14mm. This type of lens is referred to as "prime focus" or just prime for short.
f/2.8 = Maximum aperture of f/2.8, at, of course, 14mm.
L = The designation for Canon's "pro level" lenses
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