What is Inter system testing ?

It means that,sharing the resources of one system with
another. Eg:Suppose u have icici bank debit
card.OK.unfortunately u need a cash very urgent,u found sbi
atm nearby u.OK.U just and insert icici card and enter ur
pin.OK.

what the process will happen is.

The request u made is first it sents to sbibank server and
then transfers to icicibank server and process will do in
iciciserver and again it sents to sbibank server.now u can
get cash from atm.The conclusion is sbibank server is
sharing the resources with icici bank server and performing
the required operations.

Intersystem testing is the process in which wheather the one
system of resources is sharing with another system resources
or not

I hope u clear