Pass Through
HDMI cables carry audio and video signals with a single connection.
A pass through port for HDMI or any other signal simply forward the input signal, usually without changes. For an HDMI example, an AV receiver takes inputs from devices such as DVD players and cable and satellite receivers. It reads the audio signals from a selected input, amplifies them and sends them to external speakers, while "passing" the signal "through" to the viewing screen. Some AV receivers may remove the audio signal while passing through the video, but HDMI users consider this "pass through" because the video portion of the signal remains unchanged.