I'm not sure if these terms are interchangeable or not. What's the difference between ICSP and ISP? Is it simply the reset? I've shown two configurations in this question I just asked. Are they both ICSP?
According to the Atmega32U4 datasheet:
The device is manufactured using ATMEL’s high-density nonvolatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-chip Boot program running on the AVR core.
I can't find the word "ICSP" in the datasheet. The quoted paragraph doesn't really explain the acronym. It could be an anagram of SPI. ;)
It seems clear to me that "in system" and "in circuit" are referring to the same thing. The program is serial rather than parallel as it uses SPI (Serial Peripheral Interface).
I've shown two configurations in this question I just asked. Are they both ICSP?
Not really two configurations, because the ICSP header on the board is directly connected to the pins you showed in the other configuration. You may as well talk about using different ground pins as a "different configuration".