Can you mention the difference between SEO and SEM?

[Martinricky]

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.

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.