Step 1: Understand freezing point depression.
Freezing point is the temperature at which solid and liquid phases of the solvent coexist in equilibrium.
Step 2: What equilibrium exists at freezing point?
At freezing point:
\[
\text{liquid solvent} \rightleftharpoons \text{solid solvent}
\]
Solute does not form solid phase at that stage; the solid formed is pure solvent.
Step 3: Conclusion.
Therefore, equilibrium is established between liquid solvent and solid solvent molecules.
Final Answer:
\[
\boxed{\text{liquid solvent and solid solvent}}
\]