IOD (Information Object Definition)

The DICOM template of tags required for a given object type, such as a CT Image.

An IOD is the DICOM “schema” for a kind of object — it lists which tags (modules) are mandatory, conditional, or optional for, say, a CT Image or an RT Structure Set. Conformance and IOD validation check a file against the IOD for its SOP Class so a downstream system won’t reject it for a missing required tag.