SEO is search engine optimization / search engine optimizer. It is procedure of strategies, policies and techniques that is utilized to escalate the amount of visitors to a website by procuring higher ranking SERP. The chances for the users to visit a website increase when the website ranks high in the organic results.
SEM is search engine marketing which is an Internet marketing type and it includes researching, placing and submitting a website to the search engine to achieve maximum visibility and increase your share of organic / paid traffic references from the search engines. SEM comprises of things like SEO, keyword research, competitive analysis, paid listing and other services delivered by search engines that draw search traffic to a website.