Often referred to as a digital certificate or a public key certificate, a certificate is a digital document that binds a public key to an identity. This document is used in various forms of online transactions and communications to prove the identity of an entity, like a person, company, or server. Certificates play a key role in public key infrastructure (PKI) systems, helping to prevent impersonation and interception by confirming that an entity is who it claims to be and thus promoting trust and security in digital communications.