It's also used to describe the rectangular mat itself, which is typically about 1.65 meters by 2.75 meters.
In a broader sense, "tatami" can also refer to the room itself where tatami mats are used as flooring.
Here are some other ways "tatami" can be used:
* Tatami-zōri: Straw sandals worn indoors.
* Tatami-ire: A tatami mat storage bag.
* Tatami-shiki: A tatami mat laying ceremony.
So, "tatami" has a multifaceted meaning, encompassing the material, the mat, and the space itself.