GRIB is the format used by all the world's operational weather centers. "The World Meteorological Organization (WMO) Commission for Basic Systems in 1985 approved a general purpose, bit-oriented data exchange format: GRIB (GRIdded Binary). It is an efficient vehicle for transmitting large volumes of gridded data to automated centers over high-speed telecommunication lines using modern protocols. By packing information into the GRIB code, messages (or records - the terms are synonymous in this context) can be made more compact than character oriented bulletins, which will produce faster computer-to-computer transmissions. GRIB can equally well serve as a data storage format, generating the same efficiencies relative to information storage and retrieval devices."
There are two GRIB versions denoted here as GRIB-1 (original) and GRIB-2 (new). Each GRIB-1 record contains information for two horizontal dimensions (eg., latitude and longitude) for one time and one level. GRIB-2 allows each record to contain multiple horizonal grids and levels for each time. A collection of GRIB records is called a GRIB file. However, there are no rules dictating the order of the collection of records.
Depending upon one's point of view, GRIB may or may not be described as "self describing." All the information necessary to unpack the data is contained within each record. However, the variable being unpacked is denoted by an "indicator parameter" and the variable's name and units must be determined by a table lookup.