< programming > A variable in a logic programming language which is initially undefined ("unbound") but may get bound to a value or another logic variable during unification of the containing clause with the current goal . The value to which it is bound may contain other variables which may themselves be bound or unbound.
For example, when unifying the clause
sad(X) :- computer(X, ibmpc).
with the goal
sad(billgates).
the variable X will become bound to the atom "billgates" yielding the new subgoal "computer(billgates, ibmpc)".
(1995-03-14)