What exactly is the different between "extensible programming" and "extendible programming?" Wikipedia states the following: The Lisp language community remained separate from the extensible language community, apparently because, as one researcher observed, any programming language in which programs and data are essentially interchangeable can be regarded as an extendible [sic] language. ... this can be seen very easily from the fact that Lisp has been used as an extendible language for years. If I'm understanding this correctly, it says "Lisp is extendible implies Lisp is not extensible". So what do these two terms mean, and how do they differ?