A very abstract idea of its relevance, insofar as I understand it; engineering generally boils down to putting together available things to create some whole, a

A very abstract idea of its relevance, insofar as I understand it; engineering generally boils down to putting together available things to create some whole, and category theory gives a vocabulary for describing how things (considered very abstractly) can be put together. So for instance, one of the big applications to CS is in type systems, which describe what kinds of expressions/values can be put together, and in what ways, to create valid programs.