1. [A] generic term encompassing decode and decipher.
2. To convert encrypted text into its equivalent plain text by means of a cryptosystem. (This does not include solution by cryptanalysis.)
Note: The term "decrypt" covers the meanings of "decipher" and "decode."
Source: from Federal Standard 1037C and from the National Information Systems Security Glossary and from the Department of Defense Dictionary of Military and Associated Terms