Public Key Infrastructure (PKI) is a framework that enables secure communication and data exchange over networks through the use of cryptographic key pairs: a public key and a private key. PKI provides services such as digital certificates, certificate authorities (CAs), and registration authorities (RAs) to authenticate identities, encrypt data, and ensure integrity and non-repudiation of transactions. It is widely used in various applications, including secure web browsing (HTTPS), email encryption, and virtual private networks (VPNs), playing a crucial role in establishing trust in digital interactions.