Definition - What does Rupadhatu mean?
Rupadhatu is a Sanskrit word that means "form realm" and refers to the world above the physical world we live in. Beings in the form realm are not sexually distinct; they do not experience desire, extremes of pleasure or pain in the way humans living in the physical world do. In the form realm, beings still have bodies, but they are very subtle and almost invisble.
Yogapedia explains Rupadhatu
The Rupadhatu is the first of the physical
realms above our world. The realms above Earth and our physical world are correlated to the level of joy the beings that exist there experience. Beings in Rupadhatu are not governed by physical sensation the way yogis on Earth are. The minds of the beings in Rupadhatu are in a constant state of dhyana, or mediation, that is divided into varying levels, based on their practice.
Rupadhatu is a multi-layered world containing different groups of beings that are able to communicate with other beings in their layer, but not with others in different layers. The layers are progressively larger as they go up, as are the beings who live there. In the Rupadhatu, there are five layers: Suddhavasa, Brhatphala, Subhakrtsna, Abhasvara and Brahma. Beings in these levels are aware of the beings below them, but not of the beings above them, which has led the Brahmas to believe they created all the worlds.