TTL
Time to live. How long a resolver may cache this answer. Seconds, not a promise the world forgets on cue.
TTL is the lifetime on a DNS record, in seconds. Recursive resolvers may cache up to that long, and they may clamp it. Zero means ask again next time, not never cache anywhere.
You cannot force the world to forget faster than the TTL you already shipped. Lower TTL before a cutover. Short TTL everywhere is a query bill and a gift to fast-flux. Long TTL on a wrong record is an outage with a clock.
See also: DNS, Fast flux, SOA record.