What does "TTL" mean in Domain name resolution?

We often see the TTL field when parsing a domain name, which is written by default at 3600.
In addition, sometimes when we ping a domain name or IP, it will appear ttl= XXX so what does the TTL mean?

What is the TTL value for a domain name?
TTL (time-to-live), which is the lifetime of a domain name resolution record in the DNS server. When the DNS server in the local region receives the resolution request, it sends the resolution request to the NS server specified by the domain name to obtain the parsing record, and after obtaining this record, the record will be stored in the DNS server for a period of time, and if the domain name is resolved again during this period, Instead of making a request to the NS server, the DNS server will return directly to the record that was just obtained, and the time that this record is retained on the DNS server is the TTL value.

Application of TTL value setting:
One. Increase the TTL value to save domain name resolution time and accelerate website access.
In general, the various records of the domain name are rarely changed, and it is likely that there will be no change in months or years. We can increase the TTL value of the domain record so that the record is cached in the DNS server for a longer period of time, so that for a longer period of time, when we visit this website, the local ISP's DNS server does not need to make a resolution request to the NS server of the domain name, but returns the domain name resolution record directly from the cache.
Domestic and international many platforms TTL values are in seconds, many of the default value is 3600, also is the default cache 1 hours, this value is a bit small, will someone one hours to change the domain name record? You can expand the value appropriately to suit your needs, such as setting the cache to 86400 a day. GoDaddy's TTL settings are intuitive, but a total of only 5 values can be selected, the instant switch to Advanced settings mode is the same, a bit inflexible. Website profit
Environment forced, lifetyper.com TTL value is set to the maximum value of 1 weeks, set to a larger value may have to write unnecessary trouble, for example, when you want to change the space, these old records will be too long to expire and be updated.
Two. Decrease the TTL value to reduce the inaccessible time when changing space.
Change of space 99.9% there will be a problem with DNS record changes, because of the cache problem, the new domain name record may be in place in some places, but in some places may wait for two days or even longer to take effect. The result is that some people may have access to the new server, and some people have access to the old server. It's not a big deal if it's just a visit, but if it comes to email, it's a bit of a hassle, and maybe an important letter is sent to the old server that has been stopped.
In order to minimize the resolution time difference around the world, it is reasonable to:
1. First Look at the current TTL value of the domain name, we assume 1 days.
2. Change the TTL value to a settable minimum, or, if possible, 1 minutes, or 60.
3. Wait a day to ensure that DNS server caches are expired and records are updated everywhere.
4. Set the new record to be modified so that the DNS can be updated to the new record at the fastest speed.
5. Confirm that DNS has been updated around the completion, set the TTL value to the value you want, ttl=60 or too small point.
Keep in mind that all of this can work if the DNS servers are fully complying with these standards and specifications, otherwise the NS server will not be able to set the TTL, but for the time being there is no such thing as a well-behaved DNS server.
The problem is that there is no real sense on the high-speed NS and DNS servers. As mentioned here, in the domestic speed performance of the million net, in the evaluation site abroad score is very low, and in the foreign evaluation to get the highest score GoDaddy, in the domestic use of speed than million net faster. If you have the money like Google, Microsoft in the world to deploy a large number of CDN Accelerator server and NS Server, of course, no problem, the problem is that most of the site is not possible, domestic and foreign not to have, but it is difficult to profit site.
Perhaps some people think that it is possible to increase the resolution speed by specifying two NS records for the domain name (one abroad in a country), but it is also impossible for the DNS server to send a resolution request to the second NS server only if it fails to obtain a record from the first NS server. One of the cheapest and most effective ways I know to speed up is to modify the TTL value of the domain name record that you just said.

What does "TTL" mean in Domain name resolution?