eBay is more than just a web site. It's a community of millions: people in all parts of the world, all of whom are buying and selling with varying degrees of experience, ingenuity, and, of course, intelligence. eBay refers to the universe it has created as the "eBay Marketplace," which is indeed an apt description.
What makes eBay great is access. As a buyer, you have access to things you can't get anywhere else: antique toys, used computer equipment, rare movie posters, handmade clothing, cheap cell-phone accessories, furniture, music, and everything in between. And as a seller, you have access to buyers all over the world, willing to shell out money for just about anything you can take a picture of.
eBay has become a vital tool for collectors of all sorts. In my first few weeks of exploring eBay, I found a rare toy train that hasn't been made since I was a kid drooling over pictures in a catalog. In fact, thanks to eBay, I rediscovered a hobby I had loved in my childhood, and met others who have done the same.