Sensitivity - Chance that the test will be positive in someone who is infected. Low sensitivity means lots of false negative results (ie, the test is negative but the person is actually infected).
Specificity - Chance that the test will be negative in someone who is NOT infected. Low specificity means lots of false positive results (ie, the test is positive but the person is not infected).
Threshold - Threshold below which a person can be assumed to be uninfected