TTL stands for Time to Live, and it is a field on DNS records that controls how long each record is valid and cached by the DNS resolver before it expires and requests a new one. The TTL value is measured in seconds, and it affects how quickly DNS changes propagate across the Internet. A lower TTL means that the DNS resolver will refresh the record more frequently, but it also increases the load on the DNS servers. A higher TTL means that the DNS resolver will cache the record longer, but it also delays the update of the record.