A state of a thermodynamic system in which the sum of the forces, and torque, on each particle of the system is zero
Particularly in fluid dynamics it means that fluid pressure
is defined for any spatial location LaTeX Math Inline body p(t, {\rm r})= \rm const
at any moment of time LaTeX Math Inline body \bf r
and it stays the same at all locations and not changing over time LaTeX Math Inline body t