PKCS#12

PKCS#12 is a PKCS (Public Key Cryptography Standards) developed by IBM and published by RSA Security. It is designed as the Personal Information Exchange Syntax Standard. This means that it serves as a standard to exchange sensitive key information between one kind of keystore and another kind. In Java you can instantiate a Keystore in the standard way Keystore.getInstance("JKS") or with a PKCS12 SPI implementation Keystore.getInstance("PKCS12"). Both implementations store private keys and certificates in a single file. OpenSSL however, stores them in separate files. Via the 'openssl pkcs12' command you can merge them into a PKCS#12 file, bridging the cap towards a Keystore. For instance:

openssl pkcs12 -export -inkey newSignedRequest.pem -certfile myCertFile.pem -name "TEST CERTIFICATE" -out myPkcs12Cert.p12

Certificates comming from a CA are almost always delivered in pkcs12 format.