A USB CDC (Communication Device Class) Serial Port Emulation driver allows Windows to recognize and communicate with devices that emulate a traditional serial port over USB. These devices, such as certain microcontrollers, development boards (e.g., Arduino, Raspberry Pi), or other USB-to-serial adapters, use the CDC class to provide a virtual COM port (serial port) interface, allowing software to interact with them as if they were traditional serial devices.
In simpler terms, the USB CDC Serial Port Emulation driver makes it possible for your computer to communicate with USB devices using the standard serial port protocols (RS-232, RS-485, etc.), even though the device is connected via USB instead of a physical serial port.