How is SEO different from SEM?

SEM: The paid listings on the top (above SERP results) and on the right side of results are simply sponsored listings, AKA ads.

SEO (Natural Results) - The natural, organic results that are found when a user searches certain terms are ranked in order of relevance and importance.

There is a lot of debate currently going on regarding SEO and SEM and the differences between them. SEO stands for search engine optimization while SEM stands for search engine marketing. First, let’s cover the basic definition for SEO.
SEO includes natural methods of making a website search engine friendly. Changes are made to the website itself for the purpose of trying to make search engines recognize the website as important and popular. Every search engine uses algorithms (mathematical processes), to determine how popular and important a website is. The search engine then uses these algorithms to determine where a website shows up in the search engine results when specific keyword terms are searched by users.

Search Engine Optimization vs. Search Engine Marketing: SEO is actually a piece of SEM, part of the process. SEO is everything you do to optimize a website for organic search ranking. It's certainly the cheapest way to drive traffic when done right but SEM doesn't stop there. SEM is everything you do to market your site on the internet. This includes organic SEO, paid traffic, submitting your site to search engines & directories, PPC campaigns, link building, web analytics, & monetization of the site.

SEO stands for ( Search Engine Optimization) and SEM stand for (Search Engine Marketing). There is little bit difference between both of these. SEO makes websites friendly with search engine by natural methods while SEM takes advantages of the other online marketing resources which are available to them.

SEO is free link building and SEM is paid Marketing just like bill boards!

Thanks for your good post and Will be back to chech out more posts keep up the great work!