I don't believe that I ever heard the term "leaf peeping" before last year, but that just means that I've been living under a rock. Wikipedia says the term was used in the West Wing and the Sopranos, so it's been around for a while.
I wasn't intending for my October trip to be a Leaf Peep activity, but that's what ended up happening. And given that it was the anniversary of that time when I persuaded my family to do a girls trip on Scout Camp weekend, I'm now officially declaring that the third weekend in October is Leaf Peep Weekend.