What is lisp in AutoCAD?

A lisp routine is a short program you write to do perform a specific action in ACAD. All the commands are LISP routines. If you want to know how, the internet is full of examples and it is really very easy and if you have made a lisp and it works.... it feels great!

Lisp is like a plugin. which runs different commands which are not available in AutoCAD.

"AutoLISP is a dialect of Lisp programming language built specifically for use with the full version of AutoCAD" Wikipedia.

Personally I do not use AutoCAD since is a software used mostly for Architecture or Industrial Design. Therefore I decided to copy/paste the answer from Wikipedia.

Auto-LISP is a small, dynamically scoped, dynamically typed LISP dialect with garbage collection, immutable list structure and settable symbols, lacking in such regular LISP features as macro system, records definition facilities, arrays, functions with variable number of arguments or let bindings. Aside from the core language, most of the primitive functions are for geometry, accessing AutoCAD's internal DWG database, or manipulation of graphical entities in AutoCAD. The properties of these graphical entities are revealed to Auto-LISP as association lists in which values are paired with AutoCAD "group codes" that indicate properties such as definitional points, radii, colors, layers, line types, etc. AutoCAD loads Auto-LISP code from .LSP files.

I think Mr. Kinsbergen answered it very well and I have nothing to add

1. AutoLISP is a dialect of Lisp programming language built specifically for use with the full version of AutoCAD and its derivatives, which include AutoCAD Map3D, AutoCAD Architecture and AutoCAD Mechanical.

I agree with Mr . Wolf Kinsbergen answer ...thanks

api...attributes data ...to autocd

autolisp is a dialect of  lisp programming language specifically use with the full version of autocad and its derivative 

its a system generated code.