A table of interrupt vectors (pointers to routines that handle interrupts). On PCs, the interrupt vector table consists of 256 4-byte pointers, and resides in the first 1 K of addressable memory. Each interrupt number is reserved for a specific purpose. For example, 16 of the vectors are reserved for the 16 IRQ lines.
An interrupt vector table is also called a dispatch table.
Also see the list of IRQ numbers in the Quick Reference section of Webopedia.