An ExtensionPoint is a point where some code can integrate, via a hook / signal / event / handler / interface / etc. ,  to another piece of code. The wording is often used when talking about modular piece of software that can integrate nicely with other pieces, often called plugins or modules. The integration is done via the ExtensionPoint''''s.

The hard part, I guess, is defining the right ExtensionPoint''''s that will be needed and make sure that they can be used in a versatile manner.

See EclipseIde

--MathieuGervais
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I learned recently an old term for this: "User Exit"

''How is this related to the idea of FrameWork''''''s?''

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Examples:

UseCase
* http://www.visualcase.com/kbase/use_case_extension_points.htm
Eclipse
* http://www-128.ibm.com/developerworks/library/x-wxxm29.html
FAQ
* http://wiki.eclipse.org/index.php/FAQ_What_are_extensions_and_extension_points%3F