A polycategory is like a category or a multicategory, but where both the domain and the codomain of a morphism can be finite lists of objects rather than just single objects.
A (multicolored) PROP can also be described as a polycategory; what distinguishes a polycategory from a PROP is that in a polycategory, we can only compose along one object at once. That is, we have a composition operation
but not an operation such as
Polycategories provide a natural categorical semantics for linear logic.
A polycategory that is “representable on both sides”, meaning informally that morphisms in $Hom(A_1,\dots,A_n;B_1,\dots,B_m)$ correspond to morphisms $A_1 \otimes \cdots\otimes A_n \to B_1 \invamp \cdots \invamp B_m$, is a linearly distributive category. A formal definition can be found in (Cockett-Seely).
M.E. Szabo, Polycategories, Comm. Algebra 3 (1975) 663-689. DOI
Robin Cockett, Robert Seely, Weakly Distributive Categories, Journal of Pure and Applied Algebra, 114(1997)2, pp 133-173 (ps.gz)
Richard Garner, Polycategories via pseudo-distributive laws, arXiv