We’ve now seen all sorts of things that exist in the Wolfram Language: lists, graphics, pure functions and much more. And now we’re ready to discuss a very fundamental fact about the Wolfram Language: that each of these things — and in fact everything the language deals with — is ultimately constructed in the same basic kind of way. Everything is what’s called a symbolic expression.
Symbolic expressions are a very general way to represent structure, potentially with meaning associated with that structure. f[x,y] is a simple example of a symbolic expression. On its own, this symbolic expression doesn’t have any particular meaning attached, and if you type it into the Wolfram Language, it’ll just come back unchanged.
f[x, y] is a symbolic expression with no particular meaning attached:
The symbolic expression List[x, y, z] displays as :
