Cryptography is the science or study of codes and ciphers. Data that can be clearly read and understood is called plaintext or cleartext. The method of disguising plaintext in such a way as to hide its contents is called encryption. Encrypting plaintext results in unreadable garbage called ciphertext. You use encryption to ensure that information is hidden from anyone for whom it is not intended. The process of reverting ciphertext to its original plaintext is called decryption.
A mathematical function known as a cryptographic algorithm, or cipher is employed, together with a key (a word, number, or phrase), in the encryption-decryption process. The same plaintext will encrypt to different ciphertext depending on the key.
It is clear then, that the security of encrypted data is entirely dependent on two things: the strength of the cipher and the secrecy of the key.
For information on encryption see...