This variable is the unique identification for a managed care organization (MCO) enabling the entity to provide coverage to eligible Medicare beneficiaries.
The first character of the contract ID is a letter that indicates the type of plan. For local managed care contracts, it begins with 'H' or '9'; for regional managed care contracts, it begins with 'R'; for prescription drug plans (PDPs), it begins with 'S'; for fallback contracts, it begins with 'F', for Employer- Direct PDP and Employer-Direct PFFS it begins with 'E'. The remaining 4 digits are numeric.
You need to know both the contract number and plan benefit package number (CNTRCT_PBP_NUM) in order to identify the specific plan in which a beneficiary was enrolled.
Source: Medicare Advantage Organizations (MAOs)