“Prox” often refers to proximity cards or proximity technology used in access control systems. HID Fargo Prox Compatible card typically use radio frequency identification (RFID) or similar technology to allow access to secure areas when waved or held near a card reader.
“Prox Compatible” card, it likely a card that is compatible with proximity card readers or systems. These cards usually have an embedded RFID chip or other technology that can communicate with the card reader.