DEM files from ingame console record

okay so i found the files from the in game record command that you enter in the console to get a demo or hackers or in my case, killing dizzy. WTF is DEM?? I can't open it in anything and i can't open it with hl2 which is what its supposed to be opened with. Seriously need some help with this shit.

idiot... lol
in console type playdemo <name of demo>
make sure the file is in cstrike folder