SEM and SEO are related but there are some differences. First of all SEM or search engine marketing has a broader scope than SEO. It is actually an amalgamation of SEO and paid search. Though initially SEO fell under the purview of SEM, it has changed with time. Now search engine optimization advertising is the only thing SEM is concerned with. SEO has separated and gone its own way. But still the two remain quite integrated when you consider the bigger picture.
It is easy to Think of SEO and SEM as interchangeable, but they are not, SEO deals exclusively with bettering your website and optimizing it in such a way that your website climbs the ladder in search engine results with ease. SEO companies are always trying to hoodwink the search engine algorithms and spiders without breaking any rules. SEM’s only concern is to generate traffic through strategically placed ads. A website should have a bit of both if it wants long term success.
An website with exceptional SEO will be able to gain traffic and ranking over time, but if it doesn’t have a good SEM structure in place, it will still miss out on quality traffic. On the opposite side a SEM driven website that spends a lot on search engine optimization advertising will generate traffic quickly but the rush might not be sustainable without a good SEO strategy to fall back on.
SEO is concerned with generating natural, organic traffic for the website by getting into the good graces of the numerous search engines. SEM is concerned with grabbing the best ad spaces in the web for your website. SEM is precise as you can target the right kind of audience, but you also pay for the privilege every time someone clicks on the ads. SEO on the other hand is more cumbersome and isn’t specific. It will get results, but the time period might be longer. Also it is very easy to change SEM strategies at a moment’s notice, changing SEO strategy takes more time and planning.