What are the differences and implications of divorce (talaq), khul' (divorce at the instance of the wife), and annulment (faskh)?

Divorce is the dissolution of the marriage contract by uttering the word "divorce" or similar expressions. Legally, it is a separation between spouses in exchange for a consideration intended for the husband. Annulment (faskh) is similar to divorce in dissolving the contract, except that annulment is a revocation of the contract, whereas divorce does not revoke the contract but rather terminates its effects. The difference between divorce and annulment is that if annulment occurs before consummation, there is no dower (mahr), whereas if divorce occurs before consummation, she is entitled to half the dower.