  Notions of `operad' and `multicategory' abound. This work provides a single
framework in which many of these various notions can be expressed. Explicitly:
given a monad * on a category S, we define the term `(S,*)-multicategory',
subject to certain conditions on S and *. Different choices of S and * give
some of the existing notions of operad and multicategory. We then describe the
`algebras' for an (S,*)-multicategory and, finally, present a tentative
selection of further developments. Our approach makes possible concise
descriptions of Baez and Dolan's opetopes and Batanin's operads; both of these
are included.
