You know that DNS powers the internet as everyone uses it today. DNS is the system that converts easy to understand domain names into the IP addresses that computers use to communicate with each other. That said, without TTL the DNS system would still be stuck as a theoretical idea.
Well, TTL is the shorthand for Time To Live and is in essence the capability of a DNS server to keep for future use, or include in its cache, DNS records. TTL is the amount of time for which a DNS record can stay in the cache of a DNS server after the DNS server has looked up the IP address for the domain name.
So, by specifying a TTL setting for a domain a website owner basically defines how often the website content is updated. A long TTL means that domain resolution is quicker because it is more likely the DNS data is still cached. TTL values can be set from a single hour, to many hours. If a website owner is not planning on changing DNS records anytime soon, a long TTL setting is just fine.
However, if the DNS records of a domain need to change in the near future it is worth decreasing the TTL entry to just a couple of minutes. This will avoid outdated DNS data getting stuck on DNS servers.