Certificate authority (CA) - is an independent subject, which issues certificates and provide services connected with its usage. If communicating parties have trust in CA, they can be sure that person on the other side is really the one, which it claims to be. Similarly it passes for servers or applications.
Certificate - is a digital confirmation binding real subject with his public key. Basic data listed in the certificate are thus public key and identification of subject. Except this the certificate contains unique seriál number of certificate, certificate validity period, identification of issuer of the certificate and other information. Certificate is digitally signed by a certificate authority.
CRL (Certification Revocation List) - a list of revocated certificates. The list is regularly updated and is available online. Included are certificates, which have been revocated upon the request of their owner or some other subject. Requests for revocation are passed for example in reasons when the private key had been revealed.
Systems with asymetric keys - cryptographic techniques for encryption of data and digital signing which use pair of keys. One of the keys is used for encryption of the data or to verificate digital signature and the second key for decryption of the data or for creation of digital signature. Only one of the keys (private key) is kept secret, while the second key (public key) is made public via paper and electronic media (for example via certificates).
Electronic signature - a short digital data item of stated length, created by cryptographic transformation of the digital message or data file and from the private key of the signing subject.