The infrastructure needed to support the use of Digital Certificates. It includes Registration Authorities, Certificate Authorities, relying parties, servers, PKCS and OCSP protocols, validation services, revocation lists. Uses include secure e-mail, file transfer, document management services, remote access, web-based transactions, services, non-repudiation, wireless networks and virtual private networks, corporate networks, encryption, and e-commerce.
Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html