Camera Lenses - Jargon Explained | DSLRBlog:

Back in my early photography days, when I was learning what it all meant (the hard, but good way - all manual), it took me ages, and many library books to get to grips with what all the various numbers meant.

Even now, I stumble over the explanations when talking to someone else - it's almost like my understanding of the numbers has become instinctual.

That said, a refresher now and then doesn't hurt - at the very least, it's given me some new terms to use when trying to explain to my other half why, exactly, I want to buy that new lens...