Backspace is the key that moves you backwards towards the start of the line. On a computer it usually rubs out the character just behind the cursor as it goes. On an old typewriter it only moved the carriage back one space; the ink stayed on the paper, and you could type over the old letter. That is why the name is space, not “delete”: the first job was to go back one space. People also use it as a verb: “Just backspace that.” Informal, everyday machine talk. Though actually, students mix it up with Delete all the time: Backspace typically takes away what is to the left of the cursor; Delete takes away what is to the right. On phones the same idea is often just a back-arrow key, and people still say “hit backspace”.