SSL Certificate Terminology
SSL has been around for long enough you'd think that there would be agreed upon container formats. And you're right, there are. Too many standards as it happens. So this is what I know, and I'm sure others will chime in. .csr This is a Certificate Signing Request. Some applications can generate these for submission to certificate-authorities. The actual format is PKCS10 which is defined in RFC 2986 . It includes some/all of the key details of the requested certificate such as subject, organization, state, whatnot, as well as the public key of the certificate to get signed. These get signed by the CA and a certificate is returned. The returned certificate is the public certificate ( not the key), which itself can be in a couple of formats. .pem Defined in RFC's 1421 through 1424 , this is a container format that may include just the public certificate (such as with Apache installs, and CA certificate files /etc/...