Many people feel SEO and SER is the same thing, but they are most defiantly not. It is like comparing apples and oranges. Both are fruit but one is soft and the other is hard. One is red and the other is orange. You can eat the outside of an apple but not the orange. Ok, I was just doing all that for fun. Basically search engine optimization and search engine relevancy both try to get you rankings, but how they do it is where the confusion comes in.
Let's look at on page factors first. SEO is about code manipulation and keyword densities, where SER is about topic relevancy and page clarification. Optimization will edit content to fit your keywords on the page, while relevancy will provide content that supports the terms by writing naturally. SEO will optimize keyword tags by getting the most powerful terms represented the best, while SER will use meta tags to tell the engines what the page is about without forcing the terms.
Now lets look at some off page factors. Optimization will buy links and trade links with any site that is similar. Relevancy will only look for topic relevant one way links, while out outbound linking to relevant sources. SEO will submit your site on a regular basis to all the engines while SER will initially submit your home page and let the spidering happen naturally like the engines like. There is not need to constantly submit your whole site over and over. They will find you just the same.
To summarize search engine optimization is more about forcing keywords on pages in the code and body to be better seen by the engines. Search engine relevancy is about becoming a resource and not just for the engines but for the users.
SEO vs. SER Round 2