Imagine you have a glass of ice water. If you refrigerate it to keep the temperature at exactly 0°C (32°F), will the water freeze or will the ice melt?
The answer is yes. What? Well, 0°C is the equilibrium point. Some of the molecules from the water will join the solid ice, while some of the molecules of water in the ice will join the liquid water. The two changes balance each other, so the glass will continue to have both ice and liquid water for as long as the temperature stays at 0°C.