The Hubble Deep Field (HDF) is an image of a small region of the sky (a Survey Field, within constellation Ursa Major) taken over a very long exposure with the Hubble Space Telescope aiming to image as distant galaxies as possible.
The HDF region of the sky has been studied at other Wavelengths in order to associate other signal with the HDF visual images.
Deep Field (DF)
Hubble Deep Field South (HDF-S)
Molecular Deep Field