To be invalid (of an ablution, prayer or fast); to be ceremonially defiled (of a person).
If a person eats or smokes after having done ablutions or if a man happens to touch a woman before he worships he has to go back and do the ablutions again, because his ablution has become invalid.
If a person is fasting and cuts himself and blood comes out, he is defiled. His fasting has become invalid; it has no value.