SSL centificate : Java Glossary

If you want to support https: SSL/TLS secure protocol on your website, you need an SSL (Secure Sockets Layer) digital certificate. You can get them free, or you can buy them from digital certificate authorities. A certificate is just a *.pem, *.crt, *.ca-bundle, *.cer , *.p7b, *.p7s file, usually base16 encoded containing an X.509 format certificate. It contains the name of your website and your private key. It is digitally signed with the certificate authority’s private key. It also contains your private key.

If you select a certificate that is not supported by the browsers your users are using, they won’t be able to read the text unless they manually install the root certificate corresponding to your certificate.