(a) Allowable costs shall mean costs incurred by a hospital which are eligible for payment by government agencies in accordance with title 11 of article 5 of the Social Services Law. To be allowable, costs must be reasonable and must relate to patient care. Allowable costs shall not include costs for services which have not been approved by the commissioner.

(b) Commissioner shall mean the Commissioner of Mental Health.

(c) Hospital shall mean a facility providing inpatient care or treatment of the mentally ill which has been issued an operating certificate by the Office of Mental Health pursuant to article 31 of the Mental Hygiene Law and in accordance with Part 582 of this Title. New hospital shall mean a facility providing inpatient care for the treatment of the mentally ill, pursuant to this subdivision, which has no previous cost experience or operating experience. For purposes of this Part, the term hospital shall not include hospitals licensed pursuant to article 28 of the Public Health Law, residential treatment facilities for children and youth issued an operating certificate in accordance with Part 584 of this Title, and hospitals within the Office of Mental Health.

(d) Hospital fiscal year shall mean the 12-month period between settlements by the hospital of its financial accounts. Effective January 1, 1993, the hospital fiscal year shall mean the 12-month period January through December.

(e) Medicare program shall mean the Federal program of health insurance for the aged and disabled established by title XVIII of the Social Security Act, as identified in section 502.2(b) of this Title, and regulations, as identified in section 502.2(d) of this Title, promulgated thereunder.

(f) Patient day shall mean the unit of measure denoting lodging provided and services rendered to one patient between the census-taking hours on two successive days. A patient day is counted on the day of admission but not on the day of discharge. A patient day is counted when a patient is admitted as an inpatient, with the expectation of remaining overnight, but is discharged on the same day.

(g) Rate year shall mean the 12-month period during which a rate established in accordance with section 577.7 of this Part is in effect.