Russian has diminutive form (уменьшительно-ласкательная форма) and augmentative form (увеличительно-усиливающая форма). For example: человечек and человечище. But how the middle, normal form is called (человек)?
As far as I know, it's "начальная форма". And in my understanding of how form names are formed, if there was some suffix (affix, postfix, or whatever) to make this neutral form, we would have some special word for it, but there is none. It's just the form from which you start and make any other form.