NUPL is market cap minus realised cap, divided by market cap. Zero means the market collectively breaks even; 0.5 means half of current value is unrealised gain; negative means the network as a whole is under water.
Commentators divide the range into named bands, from capitulation at the bottom through hope, optimism, belief and euphoria above 0.75. The bands are descriptive labels applied to past cycles rather than anything derived, and they should be read that way.
As with mvrv, the analytical value is in describing positioning: a market with enormous unrealised profit has more potential sellers than one that is flat. It does not say when those sellers act, and reaching a historic band has not prevented further movement in the same direction.
Related: mvrv, realized-cap, supply-in-profit, sopr