What exactly is MOK in Linux for?

Upon installing Nvidia drivers I was promoted to set up a MOK password or third party drivers may not work properly, so I created one. After reboot I was presented with a blue MOK management screen with a few options in it, the first one being continue boot. So I chose this and when boot was finished, my second monitor wasn't being recognized. Remembering reading something about secure boot when initially prompted about MOK, I booted into the BIOS and turned secure boot off. Now I have my second screen back. Several questions come to mind. 1. First, what is MOK? 2. Do I need it, and if not, how do I get rid of it? 3. Was losing recognition of my second screen due to installing Nvidia drivers, or setting up MOK? 4. Can I just keep secure boot off?