The last day on the billing statement covering services rendered to the beneficiary (a.k.a. 'Statement Covers Thru Date').
The "thru" date on the claim may not always represent the last date of services, particularly for Home Health or Hospice care. To obtain the date corresponding with the cessation of services (or discharge date) use the discharge date from the encounter (variable called BENE_DSCHRG_DT).
For Part B non-institutional (Carrier and DME) services, this variable corresponds with the latest of any of the line-item level dates (i.e., in the Line File, it is the last CLM_THRU_DT for any line on the claim). It is almost always the same as the CLM_FROM_DT; exception is for DME claims - where some services are billed in advance.
Source: Medicare Advantage Organizations (MAOs)