A key ring is a file which contains multiple public keys of certificate authority (CA).
A key ring is a file which is necessary for Secure Sockets Layer (SSL) connection over the web. It is securely stored on the server which hosts the website. It contains the public/private key pair for the particular website. It also contains the public/private key pairs from various certificate authorities and the trusted root certificate for the various certification authorities. It also contains intermediate certificates from the intermediate certificate authorities.
An entity or website administrator has to send a certificate signing request (CSR) to the CA. The CA then returns a signed certificate to the entity. This certificate received from the CA has to be stored in the key ring.