The Short Definition of an Organic SEO is explained here. So let us check out meaning and small explanation of the given term, which is as follows.
Search Engine Optimization - SEO methods are used to rank webpages on top of Search engine result page (SERP), Organic SEO is a term or phrase used to describe natural ranking of webpages at top of Search results. White hat SEO or Ethical SEO is used for organic SEO.
Cloaking, Duplicate content, Keyword Stuffing, SEO spam are the kinds of Black Hat SEO, This methods violates webmaster guidelines.
SEM is a term knows as Search Engine Marketing.