Certificate chain of trust refers to the list of certificates which start from the certificate you have all the way back to the root CA. There are only a handful of Root CAs that an organization may trust. If we need to trust a certificate, we also need to trust the issuer of that certificate, and the issuer of that certificate, and so on. This goes on until we find the Root CA where its certificate is checked and determined if it is trusted. If the root CA has a valid and trusted certificate, all intermediate CAs and the server’s certificate are automatically deemed valid.