By your definition, is the Philips P89C51RD2 ISP or IAP ?

I think my definition would (if I had to give one) be:
ISP - programming is accomplished using "low-level" communication (such as jtag or SPI), processor is not operating normally.

IAP - programming is accomplished using "high-level" communication (such as serial or CAN), processor is operating normally, but possibly in a protected or special section of code.