Over at Fast Company Design, there's a great short article on the difference between a font and a typeface.
“Back in the good old days of analog printing, every page was laboriously set out in frames with metal letters. … Printers needed thousands of physical metal blocks, each with the character it was meant to represent set out in relief (the type face). If you wanted to print Garamond, for example, you needed different blocks for every different size (10 point, 12 point, 14 point, and so on) and weight (bold, light, medium).
This is where we get the terms typeface and font. In the example above, Garamond would be the typeface: It described all of the thousands of metal blocks a printer might have on hand and which had been designed with the same basic design principles. But a font was something else entirely. A font described a subset of blocks in that very typeface—but each font embodied a particular size and weight. For example, bolded Garamond in 12 point was considered a different font than normal Garamond in 8 point, and italicized Times New Roman at 24 point would be considered a different font than italicized Times New Roman at 28 point.”
I'll admit to being one of those pedants whose teeth grind when the two get confused by people who should know better. I have a slug (a clumping of metal type) on my desk that I use to explain this to my interns and minions.
For the curious, some great typography books:
And just for fun, a game to test your kerning skills: KERNTYPE, a kerning game.