Alla412, thanks for your question. That is real wood (red oak), but it is essentially an engineered flooring, with a thin ~1/4" layer of hardwood over a plywood base, for a total thickness of 5/8" or so. It is an 8 x 8 tile that is glued down to the concrete slab (in this case, anyway).

The material is pretty common in postwar NYC buildings and while this is a pre-war building, it was renovated & converted to condos in the 80s, and this flooring was installed in all of the units. We kept the existing flooring for this reno and patched in where necessary. Luckily it is still widely available, and pretty inexpensive, too.