In this sense we're talking about an Array of values... an Array formula to which you're really referring to in terms of avoidance is one where you are required to commit the formula using CTRL + SHIFT + ENTER at which point the formula becomes encased within { } - hence these are often referred to as CSE formulae (a Sumproduct can also be viewed in the same manner as a CSE Array given it is processed by XL engine along similar lines)... see the link to Colin_L's array tutorial in my signature for more info on CSE Array Formulae.