What is HtmlUnitDriver in Selenium

What is HtmlUnitDriver in Selenium ?

When I wanted to run my automation scripts on CI/CD pipeline back in 2017, I was experimenting the headless browsers using HtmlUnitDriver
Now Chrome headless picked up popularity over HtmlUnitDriver as switching from GUI browser selenium code to Chrome headless is very easy unlike HtmlUnitDriver.
Selenium automation utilized HtmlUnitDriver when it needs a non GUI mode executions on jenkins server when there is no browser installed on it or no support from docker containers.