An OIS (Oracle Integration Specifications) JSON object is part of an Airnode's config.json file.
In the OIS template, there are some fields that contain <FILL_*>. This means that the value you will be replacing this with is independent from the other fields. On the other hand, if two fields contain the same expression (e.g., <FILL_OPERATION_PARAMETER_1_NAME>), you must use the same value in them, because they are referencing each other.
The file below is a basic template for OIS. Note, that it might look differently for your particular use case. You can also check out the OISes created for the examples in the Airnode repository.