Your first step would be to go back to your client and ask him what he means by IOPS - to give you a better explanation.

IOPS are used by Amazon web services and other cloud services, and measure performance. It's a very ambiguous term, and doesn't have a specific answer because there are many variables.

I'd say he is confused:
IOPS (Input/Output Operations Per Second, pronounced eye-ops) is a common performance measurement used to benchmark computer storage devices like hard disk drives (HDD), solid state drives (SSD), and storage area networks (SAN).