It stands for "Search Engine Optimization" which means getting links to your site onto the first page of results found by a search engine. Not being on the first page is almost the same as not being found at all.
That is why when you search for framus you get sites with recipes for framus, and sites offering to import framus, and sites offering phone numbers and addresses for framus, and sites offering to find information about the sordid history of framus.
And people pay for this. Because whatever you want, they want to be on the first page of results.
SEO is a process by which, we gain traffic from natural results on search engine result page. It doesn't mean to optimizing search engines.It means optimizing our website according to search engine guidelines.It is important to gain traffic from free and natural results.