To continue with the road analogy, the road to an online purchase has many twists and forks and stops along the way. The end goal, of course, is the sale. A customer could view instructions on how to use a product, add the product to the cart, and make in to the checkout page. Each one of these steps is an event along the route that leads to a sale.
You will notice on our Holy Hand Grenade site that no price is listed on the product page; there is just a Buy Now button.
When someone clicks that button, they are interested in buying. They aren't buying yet, but they are at least curious about the price. Not yet a goal, but an event we want to track.
By tracking this event, we can find out what percentages of our visitors are checking out the price as well as the percentage who finally converted. If the percentage who clicked the button is high, our landing page is good. If it is lower, we can split test it with a new version, but it is good to test periodically either...