What is Polymorphic encryption? Well i have downloaded some cryptographic algorithm. Do there are those I didn't understand so this is my question: What is polymorphic RC4 or Polymorphic xor encryption?

I heard this in malware encryption.
Perhaps you are referring to a polymorphic virus?  This is a virus which consists of a decryption program along with the actual virus code which is encrypted.  When the virus runs and subsequently spreads, it re-encrypts itself with a different key, thereby appearing to be different each time it propagates.