Just like HDMI, DisplayPort is a digital connection for sending audio and video between computers and other devices. It's typically used to link up to monitors or projectors, but unlike HDMI, most smart TVs don't use DisplayPort. The obvious answer is to get a new, longer cable, though if you have two shorter ones, you can also use a DisplayPort coupler as an easy fix. A DisplayPort coupler joins two DisplayPort cables, allowing you to extend the total length without swapping either cable. As such, a coupler doesn't boost a signal or anything similar, so the primary use is to connect two DisplayPort cables.