A proper list is a list which ends with a null identifier. This is either NIL (CommonLisp) or '() (SchemeLanguage). Proper lists are also SingleLinkedList and EssExpressions.  Proper lists are usually found in lisp dialects or lisp like languages. 

For example, in SchemeLanguage:
 (a .(b . (c . '())))
or in CommonLisp:
 (a . (b . (c . NIL)))

LispLanguage uses SyntacticSugar to compactly print a ProperList:
 (a b c)

See also EssExpressions ConsCell SingleLinkedList

CategoryLisp