Dvd Recorder With Atsc Tuner What Does A Tuner On A DVD Recorder Mean?

What does a tuner on a DVD recorder mean? - dvd recorder with atsc tuner

Basically this is my question. I want to buy a DVD recorder. And all I really want to do is to burn a movie on my DVR and live television pictures to see if I define a tape or. And may burn from the hard drive on my computer DVD. Well, what the hell is a tuner that is what they do in basic terms please? So, what is or is ATSC? Thanks for the help.