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(emacs-lisp-intro.info)Variables

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Variables
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   In Emacs Lisp, a symbol can have a value attached to it just as it
can have a function definition attached to it.  The two are different.
The function definition is a set of instructions that a computer will
obey.  A value, on the other hand, is something, such as number or a
name, that can vary (which is why such a symbol is called a variable).
The value of a symbol can be any expression in Lisp, such as a symbol,
number, list, or string.  A symbol that has a value is often called a
"variable".

   A symbol can have both a function definition and a value attached to
it at the same time.  Or it can have just one or the other.  The two
are separate.  This is somewhat similar to the way the name Cambridge
can refer to the city in Massachusetts and have some information
attached to the name as well, such as "great programming center".

   Another way to think about this is to imagine a symbol as being a
chest of drawers.  The function definition is put in one drawer, the
value in another, and so on.  What is put in the drawer holding the
value can be changed without affecting the contents of the drawer
holding the function definition, and vice-versa.

fill-column Example

Void Function

The error message for a symbol

without a function.

Void Variable

The error message for a symbol without a value.