A certificate is a secure digital document that a website, organization or individual provides to confirm their online identity and to enable a secure connection. Certificates can also be used to digitally sign transactions or documents, and to encrypt confidential information exchanged over the Internet.
A Certificate Authority (CA) is a trusted organization that issues certificates for use by other parties. Certificates are cryptographic digital security documents used to confirm the online identities of Internet service providers (ISPs), email providers, businesses, government agencies, websites and individuals. Examples of popular CAs include VeriSign, Thawte and Geotrust (all owned by Symantec), Entrust, Comodo and GoDaddy. When an organization obtains a digital certificate, the CA confirms the identity of the organization or person receiving it.