NetCDF, Network Common Data Format: "A self-describing, machine-independent
data format that supports the creation, access, and sharing of array-oriented
scientific data. " The format is an open standard.
Noet that version 4.0 of NetCDF allows the use of the HDF5 data file format (see below).
The NetCDF format is maintained by the University Corporation for Atmospheric Research (UCAR). and its homepage for the official sources is here: Network Common Data Form. The Wikipedia NetCDF entry is also a good reference site for NetCDF and applications that use this format.
HDF4 and HDF5, Hierarchical Data Format: "The name of a set of file formats and libraries designed to store and organize large amounts of numerical data. Originally developed at the National Center for Supercomputing Applications." See the Wikipedia HDF entry