It is an engraved metal printing plate mounted on a wood backing block. The business end/face is either copper (likely*) or steel and attached to the backing block to keep it flat, easier to handle and lie flush with the rest of the type-set page in the press
.
You could use it alone or more likely with other blocks assembled to make an entire page of copy for a semi-(?)automated printing press.
Result would likely not be one/few copies but a large number of newspaper/magazine/advertising pages.

My guess of copper is that this would be a hand engraved plate easier to carve in relatively soft metal giving good results with a useful lifespan. If multiple plates were to be made for an advertising campaign, including replacement of damaged ones, it would be much easier to carve.

A steel plate would last longer but that would be decided by the time/cost equation.

See If the plate attracts a magnet &/or is red or silver/grey if scratched/cleaned on the side.

Of course I am often wrong but my opinion is only worth what you paid for it.

Best,
Lee