In fuzzy logic, a real number in the interval $\left[0,1\right]$ indicating ‘how true’ a formula is. Thus, e.g., if one takes a predicate such as ‘$x$ is bald’ to be vague, applying to individuals with varying degrees, a degree of truth between $1$ and $0$ might be assigned to the sentence ‘John is bald’ in those cases in which John is at a borderline state.