LDO is a type of regulator (which can operate with a minimal difference between the input and output voltage). POL is an application or architecture for a regulator.
Both LDOs and switching regulators are used as point of load regulators. POL generally means that the regulator supplies a subcircuit with regulated power rather than having a large regulator that supplies an entire system.
POL regulators are particularly useful when the load is noise sensitive or the voltage rail is high current. Noise sensitive circuits typically use an LDO and take advantage of the fast that the local LDO has a high power supply noise rejection factor (often other circuits that are generating the noise are also on the far side of their POL regulator further reducing the noise). High current supplies take advantage of a higher voltage on the intermediate supply rail (input to the POL regulator) creating smaller currents in the power distribution network and therefore smaller losses.
Note that there are conflicting goals here, LDO regulators are typically operated with a relatively small difference between the input and output voltages (since the voltage drop * current is dissipated as heat). With switching regulators to minimize I2R distribution losses, a much larger difference between input and output voltages is desired. Often, both are used with a switching regulator to drop a distribution rail to one or two volts above the desired output followed by an LDO to eliminate the bulk of the output noise on the switching regulator.
