The Köchel catalogue (German: Köchel-Verzeichnis) is a chronological catalogue of compositions by Wolfgang Amadeus Mozart, originally created by Ludwig Ritter von Köchel, in which the entries are abbreviated K. or KV. Its numbers reflect the ongoing task of compiling the chronology of Mozart's works, and provide a shorthand reference to the compositions. According to Köchel's counting, Requiem in D minor is the 626th piece Mozart composed, thus is designated K. 626. Köchel's original catalogue (1862) has been revised; catalogue numbers from the sixth edition are indicated either by parentheses or by superscript: K. 49 (47d) or K.6 47d. Source: Wikipedia (en)