What is warm dense matter?
matter contained within the core of gas giant planets like Jupiter
It's actually quite a recent exciting development. Discovered to be stable in the cores of gas giants like Jupiter and Saturn, it has demonstrated to have quite strange properties. Even more is believed to be found on the exo-planets recently discovered by NASA.
Not a lot is currently known about WDM because it's very hard to recreate in a lab and can only last fractions of a second, but understanding it's properties sometime in the future is key to understanding the formation of planets like Jupiter.