magic number

File Signature or “magic number” identification which is often located at beginning of file (such as the ASCII characters M and Z at the beginning of an executable file)
The term magic number has different meanings, however here we are focusing on file, hence the magic number is a constant used to identify a file format (Kessler, 2008). Detecting such constants in files is a simple way of distinguishing between file formats, basically every file has an header and a footer in order to get correctly recognized, for example a pdf file starts with “%PDF” and ends with “%EOF” while a jpeg image file begins with “0xFFD8” and ends with “0xFFD9”. These constants are called magic numbers.