A cipher is a cryptographic algorithm used for encryption or decryption. SSL and TLS protocols support a variety of ciphers used to authenticate the server and client to each other, transmit certificates, and establish session keys.
Some ciphers are stronger and more secure than others. Clients and servers can support different cipher suites. During a secure connection, the client and the server agree to use the strongest cipher that they both have enabled for communication, so it is usually sufficient to enable all ciphers.