Often confused with Search Engine Marketing, Search Engine Optimization is much different and more complicated. It requires far more skill in content and partnership work than simply in advertising or analysis.
Search Engine Optimization is the name used to describe content and marketing tactics to improve a website and page’s ranking in “Free” online searches. It involves the science of crafting the site structure, content and technical configuration appeal to Readers and Spiders alike.
Many organizations will refer to this as "free search". This comes from the fact that there are no direct advertising fees paid for the search listings when they appear. However, there is considerable investment in technical structure, content manipulation and outreach required to be successful in this area. It could be one of the most expensive free programs around!
This is an ever-evolving science and skill, often very difficult to remain under control. It is best to work with some expert outside your organization with the visibility into the changing algorithms of search engines, as well as visibility into what is working for other clients.