AutoLISP, CommonLISP, and other LISP language files
LSP is a programming language file format used by AutoLISP. LSP files contain source code information for AutoLISP, which uses LISP programming language. LSP files are used with Autodesk programs such as AutoCAD, Autodesk Map 3D and Autodesk Architectural Desktop.
Learn more about .LSP files:
Read about LISP on Wikipedia.
Search for .LSP-related questions on IT Knowledge Exchange.