One can receive a PKI certificate, or a public-key infrastructure certificate, is by digitally signing and publishing the public key bound to a given user.

Embedding the public key in a digital certificate protects it from impersonators by associating and binding a user's identity to the public key. A digital certificate is the user's public key that has been "digitally signed" by a trustworthy source trusted to sign it. And, instead of "trustworthy" you could use the word: reputable.

Certificate Server (CS)

PKI or Public Key Infrastructure

certificate authority