Key broadcasting (also known as key cloning), not to be confused with key mapping, is the passing of keys that you press to your other game windows, exactly as and when you press them yourself. ISBoxer's key broadcasting functionality is provided by Repeater and is controlled by your Repeater Profile. Key mapping on the other hand is the ability to define exactly what a particular button will do when you press it, whether that will be passing the same key to other game windows, or a host of other available Actions.
The two concepts, although related, have different purposes. Key broadcasting is best used for typing, such as entering your password during login for games that have in-client login capabilities (including World of Warcraft, Runes of Magic, EverQuest and EverQuest 2) as opposed to requiring the use of a launcher, or to enter text into other user interface panels in the game. Key mapping is best used for activating hotkeys in the game, such as casting spells, enabling Auto-follow and other modes provided by the game. Note that while key mapping can paste text from the Windows clipboard where supported by the game, key mapping cannot be used to reliably type commands into the game -- this is the purpose of the game's available key bindings.
A white or black list can be applied to ISBoxer's key broadcasting mode, specifying exactly which keys should be broadcast (white list), or which keys should not be broadcast (black list). This is configured in the Whitelist/Blacklist page of your Repeater Profile. A different white or black list can be applied at any time during gameplay via a Repeater List Action, as part of a Mapped Key.