Search engine optimization (SEO) can be described as strategies and tactics used to ensure that a site is accessible to a search engine and improves the chances that the site will be found by the search engine.
The goal of successful SEO is to obtain a high-ranking placement in the search results page of a search engine (e.g. Google, Bing, Yahoo and other search engines). Internet users often do not click through pages and pages of search results, so where a site ranks in a search is essential for directing more traffic toward the site.
The higher a website naturally ranks in organic results of a search, the greater the chance that that site will be visited by a user.
SEO is typically a set of best practices that webmasters and Web content producers follow to help them achieve a better ranking in search engine results. Some of these best practices include:
SEM is a broader term than SEO, and is used to encompass different options available to use a search engine’s technology, including paid ads. SEM is often used to describe acts associated with researching, submitting and positioning a website within search engines. It includes things such as search engine optimization, paid listings and other search-engine related services and functions that will increase exposure and traffic to your Web site.
SEM offers you the opportunity to pay based on clicks (you pay only for each click through from the advertisement to your Web site). Ads in a successful SEM campaign will be shown to those consumers specifically looking for your products or services, resulting in a higher conversion rate.