The definition of interdepartmental is between more than one department.
When the marketing department and the engineering department come together in a joint effort to design a product, this is an example of an interdepartmental effort.
Involving or representing different departments, as of a business, academic institution, or government.
Between or among departments.
I sent the memo to the accounting department via interdepartmental mail.
The memo discussed a new interdepartmental project that would require resources from nearly every group.
Origin of interdepartmental