SEO vs SEM
 

They are both marketing techniques. SEO is the process of improving a web site's rankings in search results of search engines like Google, Yahoo, and Bing. These listings are also known as "organic" listings. SEM involves driving website traffic via paid advertising. SEO helps improve organic search results while SEM focuses more on advertising.

SEO is the Search Engine Optimization, which helps in increasing the website ranking that will bring your website to the top page.
SEM - Search Engine Marketing is the one that involves in driving the traffic by the paid advertising

SEO is purely based in organic and SEM depends on paid advertising.

SEO is stand search engine optimization it is based on organic and paid but SEM Social media marketing,

SEO is the organic traffic to website and SEM is the paid service.

They both are the part of the digital marketing let me describe them both one by one:

1) SEO:- SEO is stands for the Search engine optimization. it's a process of optimizing our site to make it user friendly as well as search engine friendly. so our site can rank higher on the Search engines. it has mainly two parts 1) on page activity 2) off page activity

2) SEM:- SEM is stands for the Search engine marketing. it is the process of marketing our site on the paid platforms. yes SEM is totally stands for the paid marketing.

but both are very needed part of the digital marketing they both have their own importance in the digital marketing.

SEO is the process of optimizing your web site for organic traffic from search engines. SEM is the paid marketing process.

The difference between SEO and SEM is simply that Search Engine Optimization is part of Search engine marketing or Search marketing as it is widely known. Both processes aim in increasing visibility in search engines.