steady state
A solution that no longer changes with time -- every time derivative is zero.
A steady-state solution of a time-dependent PDE is one with u_t\equiv0 (and every higher time derivative zero too); substituting this into the heat equation, for instance, collapses u_t=k\nabla^2u to Laplace's equation \nabla^2u=0.
See also
Point table
Graph settings
Calculator