The virgule punctuation mark, sometimes called a slash or a forward slash, has a few standard uses in English, plus many other common uses that aren’t considered standard by English grammar authorities.
The established uses of virgules include the following:
- They’re used in web addresses and file paths (e.g., http://grammarist.com, c:/Program Files/Google Chrome/Chrome.exe).
- They separate lines of poetry quoted without line breaks (e.g., Glory be to God for dappled things / For skies of couple-colour as a brinded cow; / For rose-moles all in stipple upon trout that swim … ).
- A virgule separates the numerator and the denominator in a fraction (e.g., ¾).
But the virgule appears in many additional, informal uses, including the following:
- It’s often used to mean per—for example, 99 miles/hour.
- It’s often used to mean and/or (as in and/or itself)—for example, “… our Federal Highway Administration hosted forums in Denver, Phoenix, Louisville/New Albany, Hartford and Brooklyn/Queens … “ (Frost Illustrated)
- It’s sometimes used to indicate a dichotomy or a vague disjunction between two things—for example, “Its appeal cuts across the usual liberal/conservative line.” (Patriot Post) An en-dash would be conventional in these cases, but people love using the virgule this way, so we should probably accept it.