This is the most literal meaning of a \"joiner.\" It\'s a simple, passive female-to-female adapter used to connect two male HDMI cables together to form one longer cable. Key Details: Function: Physically and electrically connects two HDMI cables end-to-end. Best For: Creating a longer cable run when a single cable isn\'t long enough. It\'s a simple, cheap extension method. Important Limitations: Signal Degradation: It is a passive device. It does not boost or refresh the signal. The total length of the combined cables matters greatly. For long runs (typically over 15-25 feet / 5-8 meters for 4K), the signal can degrade, causing flickering or complete signal loss. Not a Fix for Weak Signals: If your signal is already weak, a coupler will not help and may make it worse. Specifications to look for: Ensure it is a High-Speed HDMI coupler to support 4K, HDR, and other modern formats. In short: Use a coupler only to connect two short cables. For longer total distances, an active solution is better.