Yes, 5th Density is non physical, to wich we ascend after 4th density. Sometimes when people type on the interent '5D' they refer to 5th Dimension, which is 4th density, just a different term. And it causes confusion, I see it a lot, people asking about 3D, 4D, 5D etc. But yes, those are just labels, words.

D can be reffered to as either density or dimension. So basically 4th density and 5th dimension is the same thing, just different names. Sometimes it confuses some individuals when they see 3D, 4D or 5D.