Definitions of exif on the Web:

• Exchangeable Image File. The JPEG compression mode used by most digicams.
  www.dpcorner.com/all_about/terms.shtml

• EXIF stands for Exchangeable Image File Format, and is a standard for storing interchange information in image files, especially those using JPEG compression. Most digital cameras now use the EXIF format. ...
  www.toniksupport.co.uk/glossary.html

• A metadata format developed by the Japan Electronic Industry Development Association (JEIDA) that is closely associated with JPEG. Virtually any device or software application that stores or reads JPEG files is Exif compatible.
  www.photoreview.com.au/guides/digitalphotography/digital-imaging-glossary.aspx

• Exchangeable Image File Format. Data produced by a digital camera that becomes attached to each image made by the camera, including make & model of camera, date & time, image format (eg jpeg, tiff, etc. ...
  www.photographytips.com/page.cfm/1928

• A file format used in digital cameras.
  frogprint.co.nz/help/terminology.cfm

• the file format used by most digital cameras. For example, when a typical camera is set to record a JPEG, it’s actually recording an EXIF file that uses JPEG compression to compress the photo data within the file.
  www.bytecamera.com/content/view/23/192/

• Exchangeable Image File – Image data such as shutter speed, ISO etc. are stored directly in the file generated by a digital camera. The data can be read by any application supporting “JPEG” such as web browsers, image editing applications and so on. ...
  www.pixibit.com/help/glossary.asp

• Not a lot of people know this... When most digital camera store your picture they also save extra information. This can include the basic size of the image, the date and date, the aperture, shutter speed, ISO, and most other camera settings, even the make and model of the camera and lens used. ...
  www.ackadia.com/general-interest/photography/photography-glossary.php

• A de-facto standard format for storing files containing digital photographic images and audio files. EXIF uses existing formats for data compression, including JPEG and TIFF; but it is not supported by older versions of JPEG, PNG, or GIF. ...
  msdn.microsoft.com/en-us/library/cc204488.aspx

• A common photo format, which is used by most cameras.
  www.shotaddict.com/glossary.php

• Exchangeable Image File is the file format used by most digital cameras. Essentially the images are saved on image sensors together with EXIF data containing useful information about the photo such as shutter speed, date and time, focal length, exposure compensation, metering pattern, the ...
  www.digital-landscape-photography-adventure.com/glossary.html

• (Exchangeable Image Format) enables information such as the time and date of the photograph be stored alongside the exposure.
  www.neilmcdonaldphotography.com/blog/

• A new storage, compression file format used to store images on flash memory cards and digital cameras. Exif file contain either JPEG compressed files or uncompressed TIFF files, and can contain addition header information. (Also see TIFF and JPEG)
  www.drossos.com/xtras/digital_photography/digital_photo_definitions.htm