What does the math symbol \ mean

I saw this in a question and I don't know what it means. I know it cant be / which a dividing symbol.

HELP

In mathematics, a backslash-like symbol is used for the set difference. More info about set differences below.

It is the "relative complement" operator for sets. A \ B -- things that belong to A and not to B.

Sometimes you may hear it said as A "sweep out" B. In other words, sweep out of A any elemts that belong to B.

Also, it is not commutative; i.e. A \ B ≠ B \ A

It has to be the dividing sign or symbol for ratio. It was probably a typo.

in math /means dividing

it wold be like w/out being with out
m/r miles per house

It means to divide.