NASA data products are categorized into different "Levels". These are product dependent but the following description for OMI (Ozone Monitoring Instrument) data products is a general guideline:

Level-1B  (L1B): Products containing geolocated and calibrated spectral radiance and solar irradiance data.

Level-2 (L2): Atmospheric products derived from the L1B product. One file per orbit.

L2G: Daily binned global products derived from the L2 products.

Level-3 (L3): Averaged global gridded products, screened for bad data points.

Post-Processing involves changes only in ancillary data or information.

Re-Processing indicates data processing due to changes in the Retrieval Algorithms.

See also: EOS-DIS data product levels.