ADJ is an adjustable voltage pin, used to access an adjustable resistor, adjust the voltage you need, for example, the minimum is 1.25V, but you need 1.5V general integrated voltage regulator does not have this specification, then you can use a chip with ADJ pin to access an adjustable resistor to manually adjust the voltage you need. Or according to the calculated resistance voltage division method to match a fixed resistance, produce a constant voltage you need.
There is to make an adjustable power supply, then you can, adjustable resistance connected to the external design from 1.25 or 0V (0V requires you to connect a negative 1.25 power supply in the external line, the general voltage regulator chip minimum is 1.25V) has been adjusted to the maximum withstand voltage of the chip.