Whenever I browse through the internet for advice on how to better market a website....(I don't own one at the moment but do plan on starting a few soon) I always find articles related to SEO. They all say the same thing mostly and I have tried to search for what that is...SEO as far as I know stands for Search Engine Optimization. But the question that I want to ask is what do they mean when they say have a good keyword density? Or Do proper SEO? If anyone can simplify SEO for me it would be really nice, thank you.