This ancient article (2002) at AIGA is still getting spirited comments, many of them more interesting than the article itself.
I tend to agree with k. pennino, who says:
“font – a set of characters of the same size and style containing all the letters, numbers, and marks needed for typesetting. (gosh, this would explain why we call the software we install on our computers ‘fonts’ eh?)
typeface – the DESIGN of alphabetical and numerical characters unified by consistent visual properties.”