A scenario involving a reaction at equilibrium is one where the rate of the forward reaction is equal to the rate of the reverse reaction.
A scenario involving a reaction at equilibrium is one where the rate of the forward reaction is equal to the rate of the reverse reaction. In other words, there is no net change in the concentrations of reactants and products over time, and the system is in a dynamic but stable state.
For example, consider a reaction A + B ⇌ C + D. If the rate of A + B forming C + D is the same as the rate of C + D reverting to A + B, the system is at equilibrium. This could occur when the concentrations of A, B, C, and D remain constant over time.
In a macroscopic sense, you might observe that the concentrations of reactants and products don't appear to change, even though individual molecules are continuously undergoing reactions.