It's a measure of how much customers are using a product or service compared to the total estimated market for that product or service. Now, the big question is how to optimize it. If you act on a blue ocean strategy, it's easy: you focus on your product's quality and good advertising will be simpler. Thinking otherwise, imagine you're going on a first date with someone. You did your best self-advertising possible and when leaving the restaurant, you tried to take the first move. But then... "oh, sorry, I'm dating someone else, I thought it was just a friend's dinner." Do you really want to act in a red ocean?