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.
National Center for Atmospheric Research Staff (Eds). Last modified 14 Jan 2014. "The Climate Data Guide: NASA Satellite Product Levels." Retrieved from https://climatedataguide.ucar.edu/climate-data/nasa-satellite-product-levels.