42 C.F.R. § 416.2
As used in this part:
Ambulatory surgical center or ASC means any distinct entity that operates exclusively for the purpose of providing surgical services to patients not requiring hospitalization and in which the expected duration of services would not exceed 24 hours following an admission. The entity must have an agreement with CMS to participate in Medicare as an ASC, and must meet the conditions set forth in subparts B and C of this part.
ASC services means, for the period before January 1, 2008, facility services that are furnished in an ASC, and beginning January 1, 2008, means the combined facility services and covered ancillary services that are furnished in an ASC in connection with covered surgical procedures.
Covered ancillary services means items and services that are integral to a covered surgical procedure performed in an ASC as provided in § 416.164(b) , for which payment may be made under § 416.171 in addition to the payment for the facility services.
Covered surgical procedures means those surgical procedures furnished before January 1, 2008, that meet the criteria specified in § 416.65 and those surgical procedures furnished on or after January 1, 2008, that meet the criteria specified in § 416.166 .
Facility services means for the period before January 1, 2008, services that are furnished in connection with covered surgical procedures performed in an ASC, and beginning January 1, 2008, means services that are furnished in connection with covered surgical procedures performed in an ASC as provided in § 416.164(a) for which payment is included in the ASC payment established under § 416.171 for the covered surgical procedure.
42 C.F.R. §416.2