What does HDF stand for?

Hubble Deep Field

The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, about one 24-millionth of the whole sky, which is equivalent in angular size to a 65 mm tennis ball at a distance of 100 metres.

Hierarchical Data Format File

Halogenated Dibenzofuran(s)

Human Dermal Fibroblast

Human Diploid Fibroblast