Search Engine Optimization:
Search Engine Optimization is formating your website in such a way to improve your rankings in the search results.
In the past, it just meant having the right keywords on your site. But, over the years, it has become much more complicated. Now, it embodies how your site is built, your content, how fast your site works and how other sites/engines see your website.
Simple things like increasing links to your site and posting more often on social media, can start to help boost your rankings with the search engines.