Since a previous discussion was published 15 years ago (Leichik and Shelov 1991), other studies of terminological indeterminacy and vagueness have been carried out (cf. particularly the introduction to Bhatia et al. (2005)). The authors' 1991 discussion argued in favour of vague, fuzzy, 'soft' terms, and suggested placing some basic types of this vagueness, fuzziness and 'softness' on the scale 'Determinacy vs. Indeterminacy'. The present discussion treats various term definitions and the concepts they define, with special attention being paid to the degree of indeterminacy of the definitions and of the concepts defined. Three types of fuzzy terminological definitions are described. Conceptual indeterminacy (fuzziness, softness) of the basic theoretical terms is claimed to provide commensurability of different scientific theories.