Gary Little at A NetApp Technical Diary comments:

Recently I was talking to a network guy about storage IOPS, when he asked me. What is an IOP exactly? Immediately I remembered having the exact same question when I first started seriously working with storage gear back in 2006. I knew that an IOP was an I/O Operation, and IOPS is typically meant to  be I/O Operations per second. Surely nobody really cares how many I/O’s are done per second?

Read more at: What’s an IOP, and why do I care?