Help please! "Matter-permeable window?" Why??

Matter permeable window think Scifi futuristic window. I don't understand this, and I'm very confused and maybe you could help me out. So normally a window keeps the elements out and regulates the air on the inside. I'm sure we could find a list of other things that windows do as well, but a matter permeable window. What is the point of this? If it's not going to keep the elements out and it doesn't keep air from flowing to either side of this?

In the book House of Suns by Alastair Reynolds, a character walked through this "window" to the balcony.

0:00
0:00