The tilde (~ , pronounced TILL-duh or TILL-dee and sometimes called a "twiddle" or a "squiggle") is a special character found on most keyboards and used in a wide range of IT-related applications, including mathematics, programming, file systems, directories and URL addressing.
In some operating systems, including Unix, the tilde is used to represent the current user's home directory. On Web server systems, the tilde is used by convention as the first character for any user's home directory in the file system. Since users often keep personal or business Web pages on a server under their personal home directory, you will often see the tilde as part of Web addresses. As a mathematical symbol, the tilde means "approximately" and in logic it means "not."