'backslash' originates from Modern English, specifically a compound of 'back' + 'slash', formed in the computer era to name the character that leans the opposite way to the common 'slash'; 'back-' meant 'toward the rear' and 'slash' derived (via Middle English) ultimately from Old Norse 'slá' meaning 'to strike'.

'backslash' was coined as a technical term in computing in the mid 20th century to contrast with the earlier symbol 'slash' (forward slash). 'Slash' developed in Middle English (e.g. 'slasch') from older Germanic/Old Norse roots and became the Modern English word 'slash', and 'backslash' was later formed as its counterpart.

Initially, 'slash' meant 'a cutting or striking stroke' and then came to denote the typographical mark '/', while 'backslash' was later created to denote the opposite-direction mark '\\' used in computing.