Each Certification Authority (CA) has its own root certificate. The root certificate is a self-signed certificate that identifies the SSL certificate issuer (CA).
To increase the security level of the certificates, the Certification Authorities created the intermediate certificates (for certain types of SSL certificates). The sequence of root and intermediate certificates is called "chain". Each certificate in the chain is signed by the following certificate.
Unlike "chained" certificates, "single root" certificates are signed by the root certificate of the Certification Authority. But the tendency is to switch to "chained" type because they offer a higher level of security.
