a unit of information that precedes a data object (the contents of any particular file)

On a Files--11 volume, describes a portion of a file on the volume. File headers contain information such as the owner UIC, protection code, creation date and time, and access control list (ACL).

Many file formats contain in addition to and independent from their contents a standardized header or "lead text" that is used to recognize the file format and that may contain additional information. In the case of (pixel) image files this header often contains information not directly in relation to the image data, such as the resolution.

The portion of a source code file in Dylan interchange format that specifies the library, module, and possibly other characteristics of the remaining source code in the file.