Backslash is a backward-sloping slash used to separate directories in operating systems. C:\windows\users\...
The "\" character is called as a backslash and the "/" character is called as a forward slash or just "slash" (most commonly).
It is also used in some programming languages to declare the following character must be treated in a different way. String str="example \[title\]"
In Internet, URLs are separated with a "/" (slash) sign. People sometimes use the "forward slash" term instead of slash to avoid confusion.
You can also print a backslash on the screen without pressing backslash key. Every keyboard character has an ASCII code and it is "92" for backslash character. Press and hold the "Alt" key and then press "9" and "2" respectively. (Alt + 92)
:: Origin ::
First time, "\" sign was used by Bob Bemer in 1961 to represent some Boolean operators in the ALGOL language (an early programming language used for scientific calculations). He used it in ASCII and then it became a standard key in keyboards.