A slash (/) is a punctuation mark used for various purposes. Other names for it are: stroke, virgule, diagonal, right-leaning stroke, oblique dash, solidus, slant, separatrix, slake and whack, or forward slash. A mark in the reverse direction (\) is called a reverse slash or backslash.
One use is showing how much of something is left. For example, "15/20 boxes remaining" means that there are 15 boxes remaining out of a total 20 boxes.
A slash can also mean "and". For example, "He is a writer/director" means he is both a writer and a director. It can also be interpreted as "or". For example, in the sentence "Each employee must bring his/her Photo ID", the slash (/) means "or".