In a LISP, the parenthesis are structural syntax. Where other languages use curly braces, whitespace, square-brackets, and usually a combination thereof; LISP simply uses parenthesis.
In Lisp parentheses are used as a syntax for nested lists. Lisp programs then are written on top of that with a syntax, which is structural on top of lists. Most other languages don't use a primitive data structure for encoding programs (other than text).