Personally identifiable information, commonly abbreviate PII, refers to information like a name, social security number, etc. It is sometimes a formal regulatory category and it is among the more sensitive information commonly lost in data breaches - to lose a person's medical records, for example, is more serious if there is information that can be used to tie a particular person to those records. Much of this PII is notable for not having a whole lot of content: your social security number doesn't say much about you on it's own, but it is rather an arbitrary number (originally) used to help the government organize records about you.
Capnion has developed a specialized cryptographic protocol called Ghost PII that lets businesses work with your personally identifiable information while it is still encrypted, permitting them to keep it encrypted it all times. Let me give some detail on how it works. Any really secure method of encryption should produce two different ciphertexts when applied to the same social security number twice... without homomorphic encryption, there would be no way to determine if two ciphertexts had come from the same social security number originally without decrypting. This constant need of decryption is part of what drives the breach crisis. Capnion's Ghost PII is a technique and set of software tools for encrypting data that allows linking records on encrypted identifying numbers, determing which ciphertexts came from the same social security number without need of decrypting.