This is a slash: /. Because the top of it leans forward, it is sometimes called a “forward slash.”
This is a backslash: \. Notice the way it leans back, distinguishing it from the regular slash.
Slashes are often used to indicate directories and subdirectories in computer systems such as Unix and in World Wide Web addresses. Unfortunately, many people, assuming “backslash” is some sort of technical term for the regular slash, use the term incorrectly, which risks confusing those who know enough to distinguish between the two but not enough to realize that Web addresses rarely contain backslashes.