Browser Engines
A browser engine is a core software component of every major web browser.Ā It is responsible for transforming HTML documents and other resources of a web page into an interactive visual representation on a user's device. The browser engine takes into account CSS rules to calculate the position and color of each element, or more precisely, each pixel displayed on the screen.
As a web developer you want to install multiple browsers with different engines on your computer so that you can test your website in different browsers. Ideally you also want to test on different operating systems and devices. There are also specialized tools like https://sizzy.co/ that can make development and testing easier.