What is "automatic document feed" on a printer/scanner?

I am trying to shop for a combo printer/scanner/fax and I be wondering what EXACTLY the "automatic document feed" option is to be precise build into some machines.

What is "automatic document feed" on a printer/scanner?

That's the gadget that allows you to copy a stack of papers without have to place them on the copy glass surface one at a time. You help yourself to a stack of documents, put them in the "automatic document feed" consequently press the copy button. The printer or scanner will pull respectively piece of paper through one at a time, from top to bottom, print or scan it, next spit each piece of thesis out in exactly indistinguishable order.
It's a slot or tray you put a document within, and the printer/scanner draws it in as it scans/prints it, deeply saving you from removing the one that have just be scanned and replacing it beside the next, you in recent times put the docs down in the direct you want them scanned/printed.