A quantity is identically zero if it rigorously assumes the value of zero. The word "identically" supplies 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 Resource. https://mathworld.wolfram.com/IdenticallyZero.html