It's two cards in one! Sort of. Issued by U.S. Citizenship and Immigration Services (USCIS), the so-called "combo card" combines an Employment Authorization Document (also known as a work permit or EAD) with Advance Parole permission (allowing you to travel and return to the U.S. without abandoning your green card application-in-progress.)
The net result is that recipients don't need to carry around two separate items. (The EAD was always a plastic identity card, while Advance Parole permission formerly came as paperwork.)
Before you get too excited about this, however, realize that the convenience of consolidating these two items doesn't come with much in the way of other benefits to the recipients. In particular, it:
But wait, here's a benefit! (A small one.) If you were to submit separate applications for and EAD and for AP, you would need to include two identical, passport-style photos with each application. These usually need to be professionally done, in order to meet the size and other requirements. But when filing the two applications concurrently for the combo card, you need to provide only two photos.
If you want a combo card, you don't need to specifically ask USCIS for it. Simply include both Form I-765 and I-131 with your adjustment of status application. USCIS will do the rest.
Once issued, your card will most likely last one or two years, depending on what USCIS decides. That should give you plenty of time for USCIS to make a decision on your green card application (unless, of course, the per country limitations (quotas) delay your application processing).
Once you have a U.S. green card, you will not need a separate work permit, nor will you need advance parole in order to travel.