SEM and SEO are two different things, and it’s important to fully understand why. Although SEO is the buzzword we are probably more familiar with, SEM is really probably the more relevant concern. The clue is in the “M”. SEM deals with all aspects of marketing that pertain to the search engines.* The main difference between SEM and SEO is this. SEO concerns itself with the attainment of high rankings in the search engines; SEM concerns itself with the use of the search engines in marketing.
The easiest way to understand the difference is this. You can promote any kind of web page to the top of the rankings with SEO: it could be a Blogger blog, a Website, A Youtube Video, a Facebook page, and so forth. SEM deals with the much larger picture of how you utilize the search engines as part of your marketing strategy.
So, questions such as:- what you promote, what kind of content it contains, how you present your content, how people are attracted to your content at every stage of the process, and ultimately, how they are encouraged to convert from page visitors into people who engage and interact with your content and your business, all these concerns are the concerns of search engine marketing.