I've been in the publications field for a period of about 18 years now. When I first started in the business, graphic artists were just beginning to make the transition from hand pasting elements on boards to creating computer-generated artwork. Many terms from the old days remain in use without having to be further explained. A proof can still be called a blueline and no one bats an eye. Ask someone for camera-ready art even though negatives are no longer required and it's okay; but mention the word "font" when you are speaking about a "typeface" and your hard-earned credibility is shot.
It's a common error, however; in fact, the two words are so often confused that the FontFeed found it necessary to discuss and agree on the terms they would use when writing about their very own business: typography. By their definition, a font is the "physical embodiment of a collection of letters, numbers, and symbols whether it's a case of metal pieces or a computer file." Therefore, in the most basic terms, a font is what you purchase and put on your hard drive. It's what you e-mail to another person. It's the mechanical aspect based on the original metal letter forms. A font is like a paint brush. It's one of the utensils used for making art. By comparison, the word typeface refers to the design of the letters, numbers and symbols. It's how the O looks, the T looks, the Y looks, and how they all relate to each other.
Sounds easy, but if it were that simple, we would all get it right. Here's where it gets complicated. According to Jon Tan, every design has a family name (a typeface) and a series of personal names (fonts) which refer to the individualized styles, variants, and sizes of that typeface. So, while Gotham is the typeface, Gotham Book 12 pt is a font. That makes sense; but what about Gotham Light or Gotham Light Italic? Are they fonts or typefaces? I take Jon's interpretation to mean they are fonts, but the AIGA would call them typefaces. More on this subject tomorrow.