What does this equation mean?

The physical reason liquid cooling becomes necessary at all is straightforward: air has a volumetric heat capacity roughly one four-thousandth that of water, so once a rack’s heat density crosses roughly 20–30 kW, moving enough air through the rack to hold a safe temperature rise requires impractical airflow velocities and fan power. The heat-removal budget for a cold plate loop follows directly from the sensible-heat relation: $\dot{Q} = \dot{m}\, c_p\, \Delta T$. where $\dot{Q}$ is the heat to be removed (watts), $\dot{m}$ is the coolant mass flow rate, $c_p$ is its specific heat, and $\Delta$ T is the temperature rise the coolant is allowed across the cold plate. This is the one relationship every cooling-loop sizing decision in this article reduces to: a facility either raises $\dot{m}$ (bigger pumps, more flow, more pumping power) or accepts a larger $\Delta$ T (which raises the return coolant temperature and can push a heat-reuse exchanger below its useful delivery temperature, discussed below). There is no way around the equation; every design choice downstream is a trade against these three terms.