DNS propagation is a term to describe the updating
of information across the Internet. It takes two forms: changes to your
DNS Zone and changes to your WHOIS information.
A change to your
DNS Zone information typically affects only a handful of servers, and
can be completed much more quickly. However, the WHOIS is the master record
which tells every DNS server in the world about your domain name. A
change to your WHOIS information (such as updating the Nameserver
records on your domain name) can take up to 72 hours to propagate fully.
For more information on how DNS works, check out the video below: