The Free On-line Dictionary of Computing (30 December 2018):

start of authority

    (SOA) A type of resource record used by the
   Domain Name System (DNS) to give metadata about a set of
   domain name data (the contents of a "zone file").  An SOA
   record has the following parameters:

   Serial: the zone serial number - a version number for the zone
   file.

   Refresh: the number of seconds between update requests from
   secondary and slave name servers.

   Retry: the number of seconds the secondary or slave will wait
   before retrying when an attempt fails.

   Expire: (time to live - TTL) the number of seconds a master or
   slave will wait before considering cached data out-of-date.

   Minimum: previously used to determine the minimum TTL, this
   offers negative caching.

   (2007-05-11)