The phrase "backspace button" refers to a key on a keyboard or a button on a device that allows you to erase or delete the text or characters that appear before the cursor, moving it one space back. Full definition
Yeah, I think the backspace button was the right decision on that idea. (feastingonfruit.com)
Has the backspace button on your keyboard been erased because of how much you need to edit your manuscript? (jannieoharvey.com)
Another great convenience feature with Gboard is the ability to quickly delete a word by swiping left from the backspace button. (android.gadgethacks.com)