Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext.
The keys may be identical or there may be a simple transformation to go between the two keys.
The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link.
(Source: Wikipedia)
Note: Encrypted output is base64 encoded, input for decryption should be base64 encoded too.