A false negative is when a classification or decision system gives a negative result when it should really be positive; for example if a medical diagnosis system says someone is well, when they actually have the ailment.
This is in contrast to with a true negative, a false positive or a true positive.
Used in Chap. 9: pages 120, 121, 129; Chap. 18: page 290; Chap. 19: page 305; Chap. 20: page 325