Backspace is the keyboard key that originally pushed the typewriter head one position backwards, and in modern computer displays moves the cursor one position backwards and deletes the preceding character.

In typewriters, a typist would, for example, type a lowercase letter A with acute accent (á) by typing a lowercase letter A, backspace and then the acute accent key. This is the basis for such spacing modifiers in computer character sets such as the ASCII caret (^, for the circumflex accent). Of course, ever since moving to CRT displays, backspace composition no longer works. It has to some degree been replaced with the combining diacritical marks mechanism of Unicode, though such characters do not work well on the Web, and precomposed characters should continue to be used. Some software like TeX uses the opposite method for diacritical marks, namely positioning the accent first, and then the base letter on its position.

Pressing the backspace key on a computer terminal would generate the ASCII code 08h, BS or Backspace, which would delete the preceding character. That control code could also be accessed by pressing control-H. Terminals which do not have the backspace code mapped to the function of moving the cursor backwards and deleting the preceding character would display an ^H (caret, H) when the backspace key was pressed. This sequence is still used humorously by hackers to denote a deletion, much like overstriking. Example: My slave-d^H^H^H^H^H^H^H^Hboss decided to stall the project.

The backspace is distinct from the delete key, which in paper media for computers would punch out all the holes to indicate a deletion, and in modern computers deletes text following it. Also, the delete key often works to delete other things (such as images pasted onto word processors) while backspace usually has no effect.