In grammar, a reversal of normal word order, especially the placement of a verb ahead of the subject. Questions in English are usually characterized by inversion of the subject and the first verb in the verb phrase.
Example: About the little Rawdon, if nothing has been said all this while, it is because he is hidden up-stairs in a garret somewhere, or has crawled below into the kitchen for companionship.( Vanity Fair by William Makepeace Thackeray).