dsPIC 30F2020 Primary Oscillator
The primary oscillator is the oscillator you connect externally to the device via the OSC1 and OSC2 pins. The external oscillator is either an external clock signal, external RC network or an external crystal.

Depending on what you connect to the OSC1 and OSC2 pins, the FRC could be more accurate or less accurate than the external oscillator.

See the oscillator reference, section 7.5 for detailed information.