A client connecting to a server is an example of an event, the defined function within a plugin onClientConnect is an example of a registered forward.

http://wiki.alliedmods.net/Game_Events_(Source)

http://wiki.alliedmods.net/Hidden:_Source_Events
http://wiki.alliedmods.net/Generic_Source_Server_Events
http://wiki.alliedmods.net/Generic_Source_Server_Events
http://wiki.alliedmods.net/Counter-Strike:_Source_Events
