I've often heard people say things like, "I think you should use the Garamond font on that paper.".

This is an incorrect way to say this.  A font is a specific TypeFace, in a specific size.  So to say "use Garamond" is to tell the person what TypeFace to use, but to say "use 12pt Garamond Bold Italic" is to tell them what font to use. 

''Actually, there are umpteen different typefaces called "Garamond" by their vendors, so to say "use Garamond" doesn't necessarily define what typeface is intended...''

True.  I was trying to simplify matters a little bit.

{But most people know what you mean when you say "font" even if it's not technically correct. It's a trade-off between successful communication and technical accuracy.}
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And why are the "ends" of capital-I considered serifs? This makes it look like a lower-case "L" in a san-serif type-face. The ends of the "I" are no more serifs than the bar at the top of "T". They are a fundamental shape of the character, not a mere swoosh decoration. Somebody didn't think this through. It causes lots of typo bugs.