Hi, English isn’t my mother tongue so I was asking myself that question since I first encounted a w/… Back then I was like: “What tf does ‘w slash’ stand for?” And when I found out I was like “How, why, and is it any intuitive?” But I never dared to ask that until now
Back when business was done entirely by paper, you’d have catalogues, books full of tables of things you could order with their prices. You have limited space for printing item names and those abbreviations were used there (e.g. in the 1920s).
Oh, I see. Thanks a lot for that answer :D