Mathematical Subject Classification
From WolfWikis
Mathematics Subject Classification (MSC) codes are assigned to documents by the Mathematical Reviews editors. These are the basic subject classification codes used in Mathematical Reviews. Knowing codes relevant to your subject area can help you conduct relevant searches in MathSciNet.
Codes can be found on the AMS website, as well as on AMS publications.
Specific subject codes generally have the format two-digit number, letter, two-digit number. For example:
11B05 = Density, gaps, topology
15A24 = Matrix equations and identities
More information from the AMS.
Example classification for a MathSciNet record