Q:

How do public key rings work in cryptographic applications? 

I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might (or might not) want to publish my public key to one or another of them. 
In other words, I have a basic understanding (I hope) of how PKI works and why I'd publish my public key to a keyserver so people can find me, but I'm unclear on what these different rings mean, or what their application is. 
I'm wondering what would be a good analogy for them?   Like, Google+ circles?   I am looking for a better understanding of this concept. 

A:

It's shockingly simple.  It's a file.  It has public keys in it. 
The traditional PGP Key Ring is a sequential file with a sequential list of keys in it.  It's not even a database. 
Slightly more advanced key rings, such as those used in Key Servers actually use a database. 

A:

Yes.  It's similar to your G+ Circles or Facebook lists.  Keyring is a directory of known encryption keys or Public Keys.  If you are sending a message to someone that doesn't have access to this key ring, you can't send them an encrypted message. 
Keyrings are more widely used in PGP (Pretty Good Privacy technique).