The Planck density is the unit of density, denoted by $\rho_P$, in the system of natural units known as Planck units. $1\ \rho_P \ is \approx 5.155 \times 10^{96} kg/m^3$. This is a unit which is very large, about equivalent to $10^{23}$ solar masses squeezed into the space of a single atomic nucleus. At one unit of Planck time after the Big Bang, the mass density of the universe is thought to have been approximately one unit of Planck density.
Planck Density