In the manufacturing world, the desired fit between the shaft and the hole has to specified.
Rather than type up a whole bunch of information for you, I'll point you to what you should be looking for:
ANSI Standard B4.1, Limits and Fits.
You can find all sorts of information by googling "ANSI B4.1," including an explanation of what type of fit.
Usually, if you go to a competent machinist and you tell him what kind of fit you want (press fit, interference fit, shrink fit, running fit, sliding fit, location fit, drive fit, etc) he can look in his standard fit tables and the amount to add/subtract from the basic dimensions for the type of fit you want will be found.
Edit: I see Nathan has pointed you to the _Machinery's Handbook_ - and I will too. All questions about machining, such as the one you asked, are answered therein - often in great detail.
In the edition referenced on the link to Amazon above, you'd want to start reading pp. 628 to 649.
Last edited by wyop; September 13, 2012 at 11:31 PM.