Halliday & Matthiessen (1999: 547-8):
What does it mean to say that a natural language is an indeterminate system? In the most general terms, it suggests that the generalised categories that constitute language as a system — as "order", rather than as randomness or "chaos" (let us say randomness rather than chaos, since chaos in its technical reading is also a form of order) — are typically not categorical: that is, they do not display determinate boundaries, fixed criteria of membership, or stable relationships from one stratum to another. We could refer to them as "fuzzy", in the sense in which this term is used in fuzzy logic, fuzzy computing, etc.; but we prefer to retain the term "indeterminate" for the phenomena themselves, since "fuzzy" is usually applied to the theoretical modelling of the phenomena (it refers to meta-fuzz rather than fuzz).