A quantity which rigorously assumes the value of zero is said to be identically zero. The "identically" is used for emphasis when simply stating that a quantity is (or appears to be) zero is not considered sufficiently strong. A quantity that is identically zero is said to be vanishing, or sometimes (again for emphasis) to vanish identically.
Identically Zero
See also
Almost Zero, Hidden Zero, Vanish Identically, Vanishing, ZeroExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Identically Zero." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/IdenticallyZero.html