In
testing, the quality of a test that it will indicate a
positive result if the condition being tested for does in fact exist.
Contrapose to specificity, which is the quality of a test that it will indicate a negative result if the condition being tested for does not in fact exist.
For example, the test "always indicate positive result" will have excellent sensitivity (correctly indicating all cases) but terrible specificity (giving false positives for all non-cases). Similarly, the test "always indicate negative result" will have excellent specificity (correctly indicating all non-cases) but terrible sensitivity (giving false negatives and thus failing to indicate a single case).