Ching Ch'ing, a Chinese Ch'an master, asked a monk:
-What is the sound outside?
The monk answered:
-That is the sound of rain.
The master said:
-Sentient beings are upside down, they lose themselves in pursuit of things.
It is a tiny usually wooden bank that one can sit on. It makes an angle downward and is supposed to be ideal for seiza position sitting, by taking off weight from the knees and facilitation a good posture. You canHowever it comes in different angles and sizes (ranging from 16 cm at the front and 20 cm at the back to 19 cm at the front and 22cm at it's back). I've been practising sitting in seiza position without problems for quite a while, but general knee problems force to reconsider. Have a nice day,