Mainland Travel Permit for Hong Kong and Macao Resident
The Mainland Travel Permit for Hong Kong and Macao Residents (colloquially referred to as the Home Return Permit or Home Visit Permit) is a travel document issued by the Exit and Entry Administration of the People's Republic of China. This card-sized biometric document is issued to Chinese citizens with permanent residency in Hong Kong or Macao for travel to Mainland China.
Source: Wikipedia — Mainland Travel Permit for Hong Kong and Macao Resident (CC BY-SA 4.0)