In computer programming, an S-expression (or symbolic Expression, abbreviated as sexpr or sexp) is an expression in a like-named notation for nested list (tree-structured) data. S-expressions were invented for and popularized by the programming language Lisp, which uses them for source code as well as data. wikipedia 
The name LISP derives from "LISt Processor".[10] Linked lists are one of Lisp's major data structures, and Lisp source code is made of lists.
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symbolic | BrE sɪmˈbɒlɪk, AmE sɪmˈbɑlɪk/, symbolical | sɪmˈbɒlɪkl | adjective symbolisch
The self-organizing map (SOM) is an automatic data-analysis method. It is widely applied to clustering problems and data exploration in industry, finance, natural sciences, and linguistics.