'backslash' originates from English, specifically a compound of 'back' (from Old English 'bæc' meaning 'back, rear') and 'slash' (from Middle English 'slash', originally referring to a cutting or slashing action).

'backslash' was coined in the mid-20th century in technical and computing contexts to name the character '\' introduced in character sets (notably ASCII and later Unicode). The separate words 'back' and 'slash' existed earlier and were combined to describe this new symbol; the character is also formally called the 'reverse solidus' in character-set standards.

Initially it described a slash that leans backward relative to the forward slash; with the rise of computing it came to denote a specific ASCII/Unicode character used as a path separator and as an escape character.