It used to be pretty easy, I think. These days, it’s becoming more and more abstract.
Here’s how Seth Godin explains SEO:
PASSIVE SEO is the idea that you can do things to your site (metatags, phrases, even the articles you choose to write) that will be warmly received by the search engines. As we all know, the best passive strategy is to make great stuff, but beyond that it’s pretty clear that architecting your site properly is smart. There are people far better at this than I am.
ACTIVE SEO is the act of going outside of your site to build other sites (blogs, Squidoo lenses, delicious tags) or influence other sites (links and directories) to point to you. Not just you doing it, of course, but your readers and fans and employees as well. I wrote an ebook about part of this (download for free: flippingpro.pdf).
What do you think of those definitions?
I think they’re a little off, myself. I’m not sure there’s anything passive about page tweaking and link baiting. It’s one part of the puzzle, but won’t get you anywhere at all if you don’t have any inbound links. I think SEO is tweaking pages and building link structures.
I think all SEO is active, by definition.