Let's start from defining correct terminology
- Registrar's domain-server (server with parent domain of your domain) must have glue records about nameservers of your domain, because (in shortest form) DNS is hierarchical tree, and parent must answer on question "where they are" about direct childs. Only in this case client, asking host a.b.c.d.e.f.com (host a of domain b of domain c of domain dof domain e of domain fof domain com) will get answer (from server, which have b.c.d.e.f.com domain).
What is and why glue
Glue records in parent zone provide exactly this ability: if we'll continue to use example above, in c.d.e.f.com zone definition we must have
b IN NS somename, where somename is|are hostname(s) of NSes for domain b.c.d.e.f.com (and this records must be identical to righthand of IN NS RR in domain b.c.d.e.f.com - parents and auth. servers give same info).
Glue records have extremely big value, then NSes of domain located on hosts inside served domain. Just imagine - we have to find NSes of domain b.c.d.e.f.com, placed (for simplicity - 1 NS) on names.b.c.d.e.f.com, but in order to know IP of names, we have to get zone b.c.d.e.f.com, for which task we have to know IP of names... etc. Loop.
In order to avoid such loops, glue records for domains, which have own NSes inside itself, carry additional data - IP of hostname