In a hierarchical public key infrastructure (PKI), the certification authority (CA) whose public key serves as the most trusted datum (i.e.,the beginning of trust paths) for a security domain.
csrc.nist.gov/glossary/term/root_certificate_authority
The root certificate authority (CA) serves as the trust anchor in a chain of trust.
The validity of this trust anchor is vital to the integrity of the chain as a whole.
If the certificate authority is publicly trusted (like SSL.com), the root certificate authority certificates are included by major software companies in their browser and operating system software.
This inclusion ensures that certificates in a chain of trust leading back to any of the CA’s root certificates will be trusted by the software.