Undervoltage Lockout ensures the proper behavior of the Load Switch within a specific range of input voltages. Each subsystem within the switch has operational voltage limitations therefore it is desirable to allow switch operation only in a known good range applicable to all systems. The specific voltage at which the part works properly resides between UVLO min rise and UVLO max rise. The part is definitely in lockout when V_IN is below this minimum and definitely working when past the maximum. A small area of uncertainty resides between the two voltages. Once the device is operational the trip points for lockout voltage change to some lower values as shown on the right side of the chart. There is a hysteresis component shifting the voltage to limit the possibility of oscillation.