HDF is an acronym for Hierarchical Data Format - a data file format for storing scientific data, allowing one to organize data into datasets as multidimensional arrays, and groups of objects.
HDF homepage at:
https://www.hdfgroup.org/products/
tekbasseUser guide for HDF4:
https://www.hdfgroup.org/release4/doc/UsrGuide_html/UG_Utils.html
(previous: See
http://freshmeat.net/projects/hdf/
for links to the HDF home page.)