A file type is a name given to a specific kind of file. For example, a Microsoft Word document and an Adobe Photoshop document are two different file types. While these file types are associated with individual applications, other file types, such as rich text RTF files and MP3 audio files are standard file types that can be opened by multiple programs.
The terms "file type" and "file format" are often used interchangeably. However, a file format technically describes the structure and content of a file. For example, the file type of an image file saved using JPEG compression may be defined as a "JPEG image file." The file format might be described as a binary file that contains a file header, metadata, and compressed bitmap image data.
Each file type has one or more corresponding file extensions. For example, JPEG image files may be saved with a .JPG or .JPEG extension, while Adobe Photoshop image files are saved with a .PSD extension. The file extension appended to the end of each filename provides a simple way of identifying the file type of each file. File extensions are also used by the operating system to associate file types with specific programs. The relationships between file types and programs are called file associations and define what program opens each file type by default.
You can view a list of common file types at FileInfo.com.