The Discovery Channel is an all-purpose science channel which provides programming roughly like that provided by America’s Public Broadcasting System, primarily the science programs. It would be rather like broadcasting something similar to PBS’ NOVA all day.
One also sees popular episodes of other Discovery networks’ shows on this channel. Occasionally, for example, CROCODILE HUNTER from Discovery’s Animal Planet will be shown here, but only the much older episodes (you have to get Animal Planet or Discovery’s other networks to be able to see newer episodes of specific programming).
Because so much of the programming is indeed recycled from Discovery’s other networks, I very rarely watch Discovery itself; I prefer The Learning Channel or Animal Planet, where I am guaranteed newer material.