Vanity Nameservers are nameservers that represent your reseller business to your clients, and contain your domain name, but let you still manage the domain as a separate zone from your main reseller zone.
Assuming you have premiumwpreseller.org as your reseller domain, and example.com as a property zone, the nameservers
registered for both names will look like this:
Vanity nameservers are not required, but can be a nice way to have additional market reach with each of your zone properties you manage, although they do require a little more setup up-front.
user@machine:~ $ whois premiumwpreseller.org
domain name: premiumwpreseller.org
[ ... ]
name server: ns1.premiumwpreseller.org
name server: ns2.premiumwpreseller.org
name server: ns3.premiumwpreseller.org
name server: ns4.premiumwpreseller.org
user@machine:~ $ whois example.com
domain name: example.com
[ ... ]
name server: ns1.premiumwpreseller.org
name server: ns2.premiumwpreseller.org
name server: ns3.premiumwpreseller.org
name server: ns4.premiumwpreseller.org
Vanity nameservers require you (the reseller) to setup special DNS Hostnames with your registrar called Glue Records, but do not require your client properties to do anything special.