42 C.F.R. § 415.140
Facility setting for purposes of this section means institutional settings in which payment for services and supplies furnished incident to a physician or practitioner's professional services is prohibited under § 410.26(b)(1) of this subchapter.
Split (or shared)visit means an evaluation and management (E/M) visit in the facility setting that is performed in part by both a physician and a nonphysician practitioner who are in the same group, in accordance with applicable law and regulations such that the service could be could be billed by either the physician or nonphysician practitioner if furnished independently by only one of them.
Substantive portion means more than half of the total time spent by the physician and nonphysician practitioner performing the split (or shared) visit, or a substantive part of the medical decision making except as otherwise provided in this paragraph. For critical care visits, substantive portion means more than half of the total time spent by the physician and nonphysician practitioner performing the split (or shared) visit.
42 C.F.R. §415.140