There is often confusion between SEO and SEM – but the difference is really simple. There are 3 main terms used in the realm of Search Engine Marketing (SEM), one of which is SEM the other two are Search Engine Optimization (SEO) and Pay Per Click (PPC).
SEM is the overarching category that both SEO and PPC belong to.
SEO is also variously referred to as Organic Search, Natural Search, Non-Paid Search and other terms – but SEO is the most common way to refer to it. SEO is the process of getting a website ranked highly enough in the major search engines to drive traffic to the site. Typically a site has to be within the top 10 to generate traffic and the top 5 positions generate well more traffic than the 6-10 positions.
PPC is, as the name suggests, a paid form of advertising. PPC is not limited to SEM, it actually crosses over into the more general web marketing world – this is becasue PPC is really just an advertising method that works well on the web. I put your link on my site and you pay me when people click on it. In the real world, when most people say PPC they are referring to the ads sold by the search engines within the search results that use the PPC method. Most search engines, of which Google is the most prolific, also sell PPC ads through a network of sites. The PPC or Paid Results in the search engines is their primary driver of revenue, especially for Google.