The Free On-line Dictionary of Computing (18 March 2015):
A reduction strategy which delays evaluation of
functionarguments until their values are needed. A value
is needed if it is an argument to a primitive function or it
is the condition in a conditional. Call-by-need is one
aspect of lazy evaluation.
The term first appears in Chris Wadsworth's thesis "Semantics
and Pragmatics of the Lambda calculus" (Oxford, 1971, p. 183).
It was used later, by J. Vuillemin in his thesis (Stanford,