A pastiche is a work of visual art, literature, theatre, music, or architecture that imitates the style or character of the work of one or more other artists. Unlike parody, pastiche pays homage to the work it imitates, rather than mocking it.
The word pastiche is a French cognate of the Italian noun pasticcio, which is a pâté or pie-filling mixed from diverse ingredients. Metaphorically, pastiche and pasticcio describe works that are either composed by several authors, or that incorporate stylistic elements of other artists' work. Pastiche is an example of eclecticism in art.
Allusion is not pastiche. A literary allusion may refer to another work, but it does not reiterate it. Moreover, allusion requires the audience to share in the author's cultural knowledge. Both allusion and pastiche are mechanisms of intertextuality.