Immediate release is just that. No polymers or coatings that delay the release. Common terms would be delayed, or controlled or extended release
Seems to me that some hypothetical company, perhaps a company that "specializes in oral sustained and controlled release drug products" just might be able to create a single agonist bead that mimics the plasma concentration characteristics of both an IR and ER product. One could theoretically, albeit in-artfully, refer to such a product as intermediate release.