The descriptions of the specific statistics that are written by GemStone and GBS tools are now provided as Supplemental Documentation on the GemTalk website; see https://docs.gemtalksystems.com/current/statisticsdefinitions.
When you are browsing a statistical data file in VSD, you may look up the definition in the Statistics Information window. See the section Meaning of statistics for more on this dialog.
Since the statistics that are generated depend on the version of the GemStone/S server, while the definitions are encoded in VSD, older versions of VSD may not include definitions for recently added statistics.