1.- "unmasked" interrupts?
This would be ANY interrupt that has its enable bit set.

2.- "unmasked peripheral" interrupts?
This would be an "enabled" interrupt that comes from any of the peripherals (timers, usart, ADC, MSSP etc)

3.- "external" interrupts?
This would be INT0, INT1 etc

4.- "change" interrupts?
This would be the Interrupt on change feature normally available on PortB.4-7

The interrupt flag for each available interrupt is always set when the "event" happends (timer overflows, byte comes in on the USART etc). But if the interrupt isn't "enabled" the interrupt flag won't actually cause an interrupt - the interrupt is masked.

/Henrik.