Both terms are widely used in Internet Marketing but seem confusing for a new user.
The main differences between SEO and SEM are SEO stands for Serch Engine Optimization and Search Engine Marketing respectively.
Both help website to spot in search engines, but here comes the second difference between the two. SEO is done by organic traffic and ranked in search engines whereas SEM may be completed by paid organic campaigns or by PPC.
Advertising space could be bought from SERP for SEM and no SERP payments are required for SEO.
Organic traffic increased free of cost and only by use of knowledge and strategies will be called SEO and you have to pay Google Ads for Search Engine Marketing of the website.
SEO is increasing the amount of website visitors by getting the site to appear high on results returned by a search engine. SEM is considered internet marketing that increases a site’s visibility through organic search engines results and advertising.
Both term are different one is for organic purpose and other one is for Paid advertising. SEO is always on top list compare to SEM. As every business want to get ROI when their user search for them, rather than targeting the paid advertising you can invest in SEO which will give you constant result.
Hope this will help you!