It’s process of gaining website traffic by purchasing ads on search engines.
SEM often refers to PPC or pay-per-click advertising slash marketing
SEO vs SEM
It is a method used for maximizing the number of visitors of a website by ensuring the higher position of the site by optimizing the search.
SEO is a part of SEM
It is an online marketing technique which involves promotion of the website by increasing visibility of the site in SERPs with the help of optimization and advertising.
SEM is a broad term used for traffic generation and is a umbrella term of SEO.
Difference Between SEO and SEM
SEO is continually evolving to keep up with Google's ever-changing algorithms, but one thing is constant: SEO is made up of on-page and off-page.
SEM strictly involves earning search visibility through paid advertisements on search engines like Google. While these advertisements are commonly referred to as pay-per-click (PPC) ads, there’s a slew of additional terms used for paid search or SEM activities—cost-per-click (CPC) ads, paid search ads and paid search advertising.
Launching ad campaigns with a specific audience (e.g., geographic) in mind
Creating ad groups that consist of target keyword variations
Writing relevant ad copy using these selective keywords
Setting an ad budget
Monitoring metrics like clicks, impressions, click through rates and average cost-per-click..