A long time ago, before Microsoft Word, type was printed from individual blocks broken down into specific point sizes. For instance Times New Roman was a typeface that came in 12pt and 72pt. The word 'font' related to each specific point size.

Essentially, a typeface was made up of a number of fonts. Nowadays we have drop-down menus for selecting loads of point sizes and would never consider laying out block letters from trays to print a software manual.

So mix it up and call it what you like but essentially it's all type – the stuff we see everyday without thinking about where it came from...

Here's some different faced fonts from The Letter D. A few are available from FontStruct – developed by Rob Meek.