  The development of scientometric indicators and methods for evaluative
purposes, requires a multitude of assumptions, conventions, limitations, and
caveats. Given this, we cannot permit ambiguities in the key concepts forming
the basis of scientometric science itself, or research assessment exercises
would rest on quicksand. This conceptual work attempts to spell out some
principles leading to a clear definition of "impact" of research, and above
all, of the appropriate scientometric indicator to measure it. The aim is to
stimulate a discussion aimed at a definitive convergence on the meaning and
measurement of a fundamental concept of the scientometric science.
