A steady state has time-independent concentrations because formation and removal rates balance for the species considered. Nonzero reaction fluxes can continue, so a steady state need not be chemical equilibrium. A quasi-steady-state approximation imposes this balance approximately for a fast intermediate while slower species evolve.
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In chemistry, the term "steady state" refers to a condition in which the concentrations of reactants and products in a chemical system remain constant over time, even though the system may still be undergoing chemical reactions. This concept is often used in the context of reaction kinetics and dynamic systems where reactions are occurring at measurable rates. In a steady state, the rates of formation and consumption of specific species are balanced, leading to constant concentrations.