How does Lisp let you redefine the language itself?

Question

I\'ve heard that Lisp lets you redefine the language itself, and I have tried to research it, but there is no clear explanation anywhere. Does anyone have a simple example?<

Answer 1

From the outside, looking in...

I always thought it was because Lisp provided, at its core, such basic, atomic logical operators that any logical process can be built (and has been built and provided as toolsets and add-ins) from the basic components.

It is not so much that it can redefine itself as that its basic definition is so malleable that it can take any form and that no form is assumed/presumed into the structure.

As a metaphor, if you only have organic compounds you do organic chemistry, if you only have metal oxides you do metallurgy but if you have only elements you can do everything but you have extra initial steps to complete....most of which others have already done for you....

I think.....