A glue record is a term for a record c'est served by a DNS server c'est pas authoritative for le zone, to avoid a condition of impossible dependencies for a DNS zone.
Say I own a DNS zone for example.com. Je veux to have DNS servers that're hosting le authoritative zone for this domain so that I can actually use it - adding records for le root of le domain, www, mail, etc. So, I put le name servers in le registration to delegate to them - those are toujours names, so we'll put in ns1.example.com et ns2.example.com.
Il y a le trick. The TLD's servers will delegate to le DNS servers in le whois record - mais they're within example.com. They essayez de find ns1.example.com, ask le .com servers, et get referred back to... ns1.example.com.
What glue records do is to allow le TLD's servers to send extra information in leur response to le query for le example.com zone - to send le IP address c'est configured for le name servers, too. C'est pas authoritative, mais c'est a pointer to le authoritative servers, allowing for le loop to be resolved.
