The Digital Curation Centre has released a new briefing paper on "Interoperability."
Here's an excerpt:
Interoperability is the transfer and use of information in a uniform and efficient manner across multiple organisations and IT systems. Its purpose is to create a shared understanding of data
Data exchange requires the data to be semantically matched (i.e. ensuring that the data describe the same thing) and for any differences in representation within the data models to be eliminated or meaningfully handled. Data integration is the process which takes heterogeneous data and their structural information and produces a unified description and mapping information to allow seamless access to all existing data. Interpretation of these data must be unambiguous. More generally, interoperability goes beyond data compatibility as we also need interoperable hardware, software, and communication protocols to allow data to be interpreted correctly and unambiguously across system or organisational boundaries