minimum TTL

A default Time to Live (TTL) value set in seconds for use with all resource records in a zone. This value is set in the start of authority (SOA) resource record for each zone. By default, the DNS server includes this value in query answers to inform recipients how long it can store and use resource records provided in the query answer before they must expire the stored records data. When TTL values are set for individual resource records, those values will override the minimum TTL.