  The field of model order reduction (MOR) is growing in importance due to its
ability to extract the key insights from complex simulations while discarding
computationally burdensome and superfluous information. We provide an overview
of MOR methods for the creation of fast & accurate emulators of memory- and
compute-intensive nuclear systems. As an example, we describe how "eigenvector
continuation" is a special case of a much more general and well-studied MOR
formalism for parameterized systems. We continue with an introduction to the
Ritz and Galerkin projection methods that underpin many such emulators, while
pointing to the relevant MOR theory and its successful applications along the
way. We believe that this will open the door to broader applications in nuclear
physics and facilitate communication with practitioners in other fields.
