Digital certificate helps others verify that the public keys presented by users are genuine and valid. It is a form of Electronic credential proving that the person the certificate was issued to is who they claim to be.
The certificate is used to identify the certificate holder when conducting electronic transactions. It is issued by a certification authority (CA). It contains the name of an organization or individual, the business address, a serial number, expiration dates, a copy of the certificate holder’s public key (used for encrypting messages), and the digital signature of the certificate-issuing authority so that a recipient can verify that the certificate is real. Some digital certificates conform to a standard, X.509. Digital certificates can be kept in registries so that authenticating users can look up other users’ public keys.
Digital certificates are key to the PKI process. The digital certificate serves two roles. First, it ensures the integrity of the public key and makes sure that the key remains unchanged and in a valid state. Second, it validates that the public key is tied to the stated owner and that all associated information is true and correct. The information needed to accomplish these goals is added into the digital certificate.
A Certificate Authority (CA) is an entity trusted by one or more users as an authority in a network that issues, revokes, and manages digital certificates. A Registration Authority (RA) performs certificate registration services on behalf of a CA. The RA, a single purpose server, is responsible for the accuracy of the information contained in a certificate request. The RA is also expected to perform user validation before issuing a certificate request.
A Digital Certificate is not like same as a digital signature, they are two different things, a digital Signature is created by using your Private key to encrypt a message digest and a Digital Certificate is issued by a trusted third party who vouch for your identity.
There are many other third parties which are providing Digital Certifictes and not just Verisign, RSA.
Reference(s) used for this question: Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 14894-14903). Auerbach Publications. Kindle Edition.
Gregg, Michael; Haines, Billy (2012-02-16). CASP: CompTIA Advanced Security Practitioner Study Guide Authorized Courseware: Exam CAS-001 (p. 24). Wiley. Kindle Edition.
Please refer to http://en.wikipedia.org/wiki/Digital_certificate What is Digital certificate: http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci211947… another deifination on http://www.webopedia.com/TERM/D/digital_certificate.html