On newer doors and windows that's called a grid and the glass is one piece. Older doors have individual panes that are "glazed" in using putty. The old putty must be scrapped out then the glass will fall out in your hands.
Why do you want to get the glass out?
This is an old mud room that I'm turning into a 1/2 bath. I want to replace the glass with mirror. I thought it might look cool as well as add privacy to turn the window into a bathroom mirror. Thinking about permanently blocking off the door and putting a sink in front of it. Then put a shelf underneath overtop the sink. I have already installed a new toilet on the opposite wall.