Learn in the textbookPKI and the Core of Public Key Infrastructure
DefinitionA digital certificate (デジタル証明書) is electronic data in which a certificate authority attaches its signature to vouch that "this public key belongs to this person (or this server)."
ExplanationAlso called an electronic certificate or public key certificate, it sits at the center of PKI. By checking the signature of the issuing certificate authority, the receiver can use the listed public key as the other party's own. A certificate has an expiry date and must be renewed when it runs out.
AnalogyIt is like a photo ID card: the issuing office's seal vouches that the photo (public key) and the name (owner) go together.
Memory hookIts other name, "public key certificate," tells you outright that what it certifies is the public key.