a) the action of inverting
(with an auxiliary verb) Inversion takes place in the sentence Is she here? — is, the predicate, is before she, the subject.
(for the purpose of emphasis) Inversion takes place in the sentence Never have I done that. — have, the predicate, is before I, the subject, due to never being the first word of the sentence.
See Also: twelve tone technique, serialism
Wikipedia foundation.