Objective-C allows you to define protocols, which declare the methods expected to be used for a particular situation. Protocols are implemented in the classes conforming to the protocol.
A simple example would be a network URL handling class, it will have a protocol with methods like processCompleted delegate method that intimates the calling class once the network URL fetching operation is over.
A syntax of protocol is shown below.
@protocol ProtocolName @required // list of required methods @optional // list of optional methods @end