File format refers to the way information and data is encoded and stored in a computer file.
File formats are simply ways to encode data. You can recognize them usually from their filename extensions; for example, a file with the extension .html is probably a HTML document and a file with the extension .gif is probably a GIF image file.
On Reverse Engineering, the file-format tag is used for questions about determining the file format of a given file as well as questions about reverse engineering certain file formats.
From Wikipedia:
A file format is a standard way that information is encoded for storage in a computer file. A file format specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free and may be either unpublished or open.
Some file formats are designed for very particular types of data: PNG files, for example, store bitmapped images using lossless data compression. Other file formats, however, are designed for storage of several different types of data: the Ogg format can act as a container for different types of multimedia, including any combination of audio and video, with or without text (such as subtitles), and metadata. A text file can contain any stream of characters, including possible control characters, and is encoded in one of various character encoding schemes. Some file formats, such as HTML, scalable vector graphics, and the source code of computer software are text files with defined syntaxes that allow them to be used for specific purposes.
