what is the difference between an SEO and SEM?

[Mike F]

Short answer:
Search Engine Optimization (SEO) is a method by which Search Engine Marketing (SEM) is accomplished.

SEO is a way to improve over time, the relevency of the ads that appear with the search results, to the term or terms that were searched on.

Longer answer:
If I search on "batteries" and an ad for the "Energizer Bunny" comes up _with_ the results of the search, that's an example of SEM.

It is used to spotlight (promote) companies who pay to advertise through search engine providers, to the searcher.

If I search on "batteries" and then _click_ on the "Energizer Bunny" ad that accompanies the results, then the search engine may create/strengthen an association between the term "batteries" and the Energizer company in the database.

This would increase the relevence of the advertiser to the search term used by the searcher, and increase the probability that an ad for the same company (or even companies in their business category) will display for another searcher who enters the same search term.

Another way to increase the odds that an advertiser's ad will show up with the search results is to run the search term through a set of advertizer web sites simultaneously with the general search that produces the results.

If the search term(s) are found on an advertiser's web site and their account is in good standing with the search engine provider, create/strengthen an association and show their ad!

As the association gains strength, increase the prominence of the ad on the search results page.