The acronym PKI stands for Public Key Infrastructure, which plays a critical role in cryptography by enabling secure communication and data exchange over networks. PKI utilizes a combination of hardware, software, policies, and standards to manage digital certificates and encryption keys. It ensures the authenticity, integrity, and confidentiality of data by establishing a trust hierarchy. PKI facilitates various security mechanisms such as digital signatures, secure email, and SSL/TLS certificates, forming the backbone of modern secure digital communications and transactions.