Tatami is like the Japanese version of carpet, except it’s a lot more troublesome. Tatami are woven straw mats. You can see a close up just below.
Most houses have at least a couple rooms with this as flooring. It looks really nice, but it’s also kinda fragile and easy to damage. You can wear shoes or even slippers in rooms that have this. Just bare feet or socks. A lot of furniture can’t be used too, because it might damage the tatami. Before I first came to Japan years ago, I thought that it might feel a little soft to walk on, but it’s actually quite hard. When I ask anyone, why they still use this troublesome stuff, nobody seems to know. Much like a lot of traditional Japanese stuff, you just do.