For lack of another term. Essentially, as electronics have evolved, old boats, especially wooden, have adapted to them often in a slightly different way than modern glass boats. They may be mounted in boxes, like this one on the bridgedeck, rather than installed in bulkheads as is often the case in newer boats.

It makes sense as a 3" hole, or several, can be hard to repair in wood. And in a case like this boat, probably well over 50 years old, it's seen some electronics come and go. A box like this will house a few instruments without changing the boat a lot.