SEO is the process of getting better visibility in the organic (non-paid) listing on a search engine. SEM is the process of running paid ads on a search engine and its ad networks.
Many people think one replaces the other. Not true. They are very different.
Taking Google as an example here’s how they differ..
Where do I get seen?
SEO – You may get seen on Google, Google properties such as YouTube, and Google search partners such as AOL and CNN.
SEM – Same as SEO, plus millions of third party websites that have agreed to carry Google ads. SEM also supports geo-targeting. This means you could run your ads in any region you like such as a city, a zip code, or even a radius around your office.
What gets seen?
SEO – A snippet of text that the Google spiders find on your website. This is often a Title Tag and a few lines of content.
SEM – Exactly what you want to get seen. You write your ads and you can change them anytime you want.
What does it cost?
SEO – Nothing. Well not really, you’ll need to hire a SEO firm. If you do it yourself it will take considerable time and effort.
SEM – Google displays your ad for free, you pay only when someone clicks. That’s why SEM is often called PPC (Pay Per Click).
What keywords can I use?
SEO – You need to do SEO for each keyword. If you have many keywords that can be a huge amount of work.
SEM – You can quickly and easily run ad campaigns with thousands of keywords.
Of course, for a complete internet marketing plan you need both SEO and SEM!