Directional HDMI cables have arrows on them to indicate the direction of signal flow. The arrow head on the cable should be plugged into the output device, such as a TV or monitor. This ensures that the signal is transmitted correctly from the source device, such as a Blu-ray player or gaming console, to the display device. Plugging the cable in the wrong direction won't cause any damage, but it will prevent the image or sound from being displayed on the screen. Newer HDMI models often include direction labels on the cable itself, making it easier to determine the correct orientation. So, when connecting an HDMI cable, make sure to follow the arrow direction to ensure proper signal transmission.