Indeterminacy is the state of not being fixed, and of not being knowable for sure. It is the noun that sits behind indeterminate. Philosophers use it when a sentence can be read more than one way (the indeterminacy of meaning). Scientists use it when a system has no single settled value. In ordinary English the word is uncommon; people say “uncertainty” instead. Though actually, those two are not perfect twins. Uncertainty often lives in the person — you feel unsure. Indeterminacy lives in the thing: there is no single definite answer out there to find. A weather forecast can leave you uncertain; a rule that does not say yes or no has indeterminacy built in. Formal, mainly academic.