Static discipline
From Rice Wiki
The static discipline is a discipline in computer architecture that requires all circuit elements to produce logically valid outputs, raising abstraction from analog to digital circuits.
In the real world circuits, there is no 0's and 1's, only voltage levels. For abstraction, we interpret a range of high voltages as 1 and a range of low voltages as 0.
The static discipline ensures that this abstraction doesn't run into problems/undefined behavior by forcing all circuit elements to operate on 1's and 0's. This sacrifices the freedom of analog circuits in return for the simplicity and robustness of digital circuits.