Configuration bits are a collection of specialized bits that can only be modified at program time. Configuration bits are read during reset and enable or disable hardware features in the microcontroller. The features controlled by the configuration bits include, but are not limited to, the clock source, the Watchdog Timer (WDT), the Brown-Out Detector (BOD), and the Memory Read protection. Configuration bits are not executable code. Essentially, they are fuses located in the program memory space.
Each PIC microcontroller has its own set of configuration bits. The Device Configuration section of the individual data sheets contains the definition for each of the bits. See below an example from the PIC16F18446 data sheet.
For further details on how to set the Configuration Bits consult the 3.4 Setting Configuration Bits section.