"Lacrimosa" is Latin for "weeping" or "tearful." In music, it refers to a specific section of the Dies Irae sequence in the Catholic Requiem Mass. Mozart's version, from his Requiem in D minor (K. 626), is the most famous setting. It's the last section Mozart worked on before his death in December 1791; the rest of the Requiem was completed by his student Franz Xaver Sussmayr. There's a bitter symmetry to it: the movement about weeping was the last thing Mozart ever composed. His pen stopped in the middle of the Lacrimosa, eight bars in.