Symmetric and Asymmetric Encryption

In symmetric encryption, the same key does both encryption and decryption. The key stays secret. The parties in the communication share it.

In asymmetric encryption, there are two keys. One is public, one is private. The public key is shared openly. The private key is kept secret. Data encrypted with the public key opens only with the private key. The reverse is also true.

Useful examples

Symmetric - used in disk encryption, file encryption, etc. Asymmetric - in digital signatures, SSL session establishment, etc.

A good rule of thumb. Handshakes use asymmetric encryption. The data transfer then uses symmetric encryption.