Get thyself a copy of Ivan Law's book "Gears and Gear Cutting" for an excellent introduction to the theory and practice of gears.
Briefly, 14 1/2 degrees is the pressure angle of the teeth. It refers to the angle of contact between the teeth of mating gears.
20 dp is the diametral ptich, which determines the size of the teeth. A 20 dp gear with a pitch circle 1" in diameter will have 20 teeth.
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Law of Logical Argument - Anything is possible if you don't know what you are talking about.