There are many terms which have been introduced by the field of encryption. Each of these terms are need to understand this discussion. Plaintext is the original document to be transmitted or stored on a computer system. Ciphertext is the encrypted document. The act of encryption is the transfer of plaintext into ciphertext.
Decryption is the reverse of encryption, or transfer from ciphertext to plaintext.
In order to decrypt a message, a key is required. The key contains the information to convert the ciphertext into plaintext. Single-key systems use the same key for both encryption and decryption. This notion of escrowed-keys is what is causing great debate in political realms. Whether or not the government has a right to hold a key is the central issue in the ongoing debate.