Search Engine Marketing (SEM) is area of internet marketing that focuses on promoting websites through paid listings. It aims to increase a site’s visibility by paying search engines to show it at the top of SERPs.
Each search engine has its own advertising platform and tools, but Google Ads is probably the most popular one.
SEM tools help marketing professionals optimize and manage search ads. An SEO agency would typically carry out keyword research, set a budget, and run advertising campaigns using these tools, and keep track of how well your campaigns are doing.
The goal of any SEM campaign should be to get qualified traffic to your website. It is especially useful to target keywords that you are probably not going to rank for organically (those that are too competitive).