I'm aware of the inconsistency too, since I sometimes find myself using the two terms interchangeably, although I don't think they're entirely equivalent, so I probably shouldn't...
A variable is an identifier for an object value, which could be either a boolean value, number, string, list, lambda-list, symbol or the machine address of a built in native function or operator.
In newLISP all variables are symbols but not all symbols are used as variables. For example int the following s-expression (symbolic expression):
(set 'x '(a b c))
... we have the symbols: x, a, b , c. But only the symbol x is used as variable holding a list of symbols a, b and c. In the case of x, it is is both a symbol and a variable.
Manipulating symbols - not only their variable values - is unique to Lisp. So, although any symbol in newLISP could be used as a variable, not all of them are used that way.