This is referring to the different modes that you can use on many flat-screen displays. "fill to screen" means that the device itself will stretch and if necessary slightly distort the image that you feed in, until it completely fills the entire screen.


In other words, if the dimensions of your screen are (for example) 1024 pixels horizontally and 768 vertically, but you feed it from a computer that produces an 800 x 600 image, then the display itself will "stretch" those 800 horizontal pixels until they cover 1024, and it will "stretch" the 600 vertical pixels until they fill 768 pixels.

In other words, it "scales" the video, using a built-in circuit called a "video scaler".