What is the difference between a PKCS12 keystore and a PKCS11 keystore?

I'm interested in Java-NSS libraries, and I'm reading the Sun's P11 Guide. I am confused on the following:

What is the difference between using a PKCS12 keystore and a PKCS11 keystore?

A keystore is just a keystore, right? Are there some differences? Can they be used interchangeably in any aspect?