Please note that as of October 24, 2014, the Nokia Developer Wiki will no longer be accepting user contributions, including new entries, edits and comments, as we begin transitioning to our new home, in the Windows Phone Development Wiki. We plan to move over the majority of the existing entries over the next few weeks. Thanks for all your past and future contributions.
A certificate binds a public key to a certain individual/entity. This is usually done using digital signatures: if a certificate bearing a public key and an individual's name is signed with a key pair which you already trust, then you can rest assure that the public key in the certificate really does belong to the individual named in the certificate.