In computing, an Advanced Programmable Interrupt Controller (APIC) is a more complex Programmable Interrupt Controller (PIC) than Intel's original types such as the 8259A. APIC devices permit more complex priority models, and Advanced IRQ (Interrupt Request) management.
In computing, a programmable interrupt controller (PIC) is a device that is used to combine several sources of interrupt onto one or more CPU lines, while allowing priority levels to be assigned to its interrupt outputs. When the device has multiple interrupt outputs to assert, it will assert them in the order of their relative priority
source : http://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller