How works Jetty plugin for Maven?

I am pretty new in Maven and I am working on a portal developed wiht a product named Entand (but my question is not about Entando but it is about Maven).

So, into the documentation I find this statment about Maven:

Maven takes care of all the dependencies and thanks to the Jetty plugin it can also execute the portal without a DBMS and servlet container, which do not figure in the basic prerequisites for this reason.

So I know what Maven do and, reading the documentation, it seems to me that the Jety plgin is a Maven plugin that simply scan the project for changes and automatically redeploy the webapp if any are found. This makes the development cycle more productive by eliminating the build and deploy steps.

Ok...this seems clear but what means that it is used to execute the portal without a DBMS and servlet container?