Can you mention the difference between SEO and SEM?

[parkerpowell06]

SEO - Search engine optimization is the process of affecting the visibility of a website or a web page in a search engine's unpaid results—often referred to as "natural," "organic," or "earned" results.

SEM - Search engine marketing is a form of Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages primarily through paid advertising.