A digital certificate contains a public key and a digital signature, kind of like a digital ID card.

Provides trust, because if the certificate authority trusts this person, there's a good chance we should also trust them.

A similar system is a 'web of trust' instead of a centralized cert authority. Have individuals sign each other's certificates, creating a web of trust.

X.509 format is a digital certificate for websites. https://www.ssl.com/faqs/what-is-an-x-509-certificate/