SEO is geared to acquiring natural, "organic" rankings on a business website. When the term organic is used in terms of online marketing, it is meant that these rankings are the product of unpaid advertisements that are placed in the middle of search homepages. The goal and desired end result of SEO is to optimize a website and increase the website's ranking within the engine results, like Google, Yahoo & Bing
The best part about SEO is that implementing smart tactics can be done completely free of charge. Of course, when SEO becomes more sophisticated, financial expenditures will need to be made according to the index of the search algorithm.
SEM differs from SEO in that paid advertisements are allocated in this marketing tactic. SEO is actually the first portion of SEM, whereby SEM concludes online marketing in a more sophisticated, seamless manner. The biggest difference between SEO and SEM is the assignment of sites that obtain ranking through search marketing tactics. These paid listings are not included in the canter of the engine homepage, the way the organic results are.
SEM is an ongoing strategy, while SEO is a method you use to help your rankings. It's important that you understand which of these you are utilizing- whether you are trying to build up a site in the rankings, or whether you are just using the engines as an environment to make money. Similar, but very, very different.