HDD is an abbreviation for "hard disk drive."

Before removing the HDD, remove the temperature sensor that is mounted directly on the hard drive. The sensor is attached to the hard drive using adhesive tape and a protective foam cushion.

Peel off the foam and set the sensor aside. Be gentle with the foam because you will reuse it to connect the sensor to the new HDD.

Lift the HDD out of the device and disconnect the two SATA cables from the HDD.