According to 35 organizations and the National Alliance for Health Information Technology (NAHIT), the term interoperability means:

In health care, interoperability is the ability of different
information technology systems and software applications to
communicate, exchange data accurately, effectively and consistently,
and to use the information that has been exchanged

The definition is intended to be used in policy and legal
contexts and
as a guiding principle for technical specifications. From the press
release: "In just a few short months, The National Alliance for Health
Information Technology has succeeded in building widespread industry
agreement on a definition for interoperability in healthcare, a crucial
step to ensuring that hundreds of thousands of healthcare information
technology systems will some day be able to exchange critical patient
data." Be still my heart. While all great deeds start with a first
step, it seems their definition is remarkably close to what the IEEE defines as the meaning for "interoperability." Isn't this just "plug and play" connectivity by another name?

Back in my DICOM
days, interoperability meant that one system or application could control another. I think a more accurate definition of
interoperability would be:

The ability of systems to provide
services to and accept services from other systems, and
to use the services so exchanged to enable them to operate effectively

One system passing data to another that then processes, stores or forwards that information is using an interface,
which seems to fit the NAHIT's definition. The following is a scenario
for interoperability: A medical device sends an alarm to a
clinical information system which applies the alarm and what it knows
about the patient to a rules engine, then sends a message to the
patient's physician and instructs the medical device to cease therapy.
Admittedly, that's way beyond what the NAHT is contemplating. Some vendors are already working on these capabilities.

[Hat tip: AHA News]