The DIESIS project  gives the following definition:
- "A single simulation model that interoperates with other simulations in a federation" .
- In the DIESIS context, a federate also refers to the aggregate of a simulator and its specific enhancements, e.g., certain interfaces or middleware.
- In the HLA context, this could represent one platform (e.g., a cockpit simulator) or could represent an aggregate, like an entire national simulation of air traffic flow
Other International Definitions
United Nations’ Definition