If the ion product (IP) equals Ksp, what does this indicate about the solution?

When the ion product (IP) equals the solubility product constant (Ksp), this indicates that the solution is at equilibrium with respect to the dissolution of a sparingly soluble salt. At this point, the concentrations of the ions in solution are exactly matched to the conditions specified by the Ksp, representing a balance between the rate of dissolution of the salt and the rate of precipitation of the solid.

In other words, there is no net change in the concentration of the dissolved ions and the solid salt; the system has reached a state where the forward and reverse processes occur at the same rate. This means the solution is neither growing in concentration (supersaturated) nor decreasing (unsaturated), but is stable, which is why it is described as being at equilibrium.