What is the difference between a USB port and a USB receptacle?
The USB 'receptacle' is the mechanical connector - the thing you plug a USB cable into. That consists of electrical contacts in a plastic-and-metal housing.
The USB 'port' describes the connector, communication electronics, software and any power supply electronics needed by the equipment the port is in.
For a PC, the USB port uses a connector, power supply with current control/protection, communications electronics and an OS software driver.