This is a strong coverage criterion that is required by the US Federal Aviation Administration for Level A (catastrophic failure consequence) software; i.e., software whose failure could lead to loss of function necessary for safe operation. It requires that every condition in a decision in the program has taken on all possible outcomes at least once, and each condition has been shown to independently affect the decision outcome, and that each entry and exit point have been invoked at least once.
Sources:
NISTIR 7878
from
Chilenski et al