P5 panels are like mini televisions in that they have many RGB LED lights in a grid. They come in many shapes, styles, and layouts. The P5 panels on this page have a resolution of 64x32. The number 5 in P5 stands for 5mm of spacing between each light. Thus, these panels are 320mm wide by 160mm tall. By utilizing more than one P5 panel, you can daisy chain them together to make much larger panels that behave as one. Each purchased P5 panel comes with a short ribbon cable to daisy chain to a second panel, and a power cord for every two panels (pictured in the gallery above). If you purchase one or two panels, you receive one power cord that will power two. If you purchase three or four panels, you will receive two power cords that will power up to four panels... and so on.
Below is a great video that explains what a panel is and some of the different ways in which you can run Panels. The second half of the video focuses directly on Colorlight Cards and their configuration. NOTE: The configuration steps in this video are outdated. Both FPP and LEDVision have been through multiple versions since this video. A direct link to the video can be found here: http://videos.xlights.org/xessentials-e26-p5-p10-panels-and-the-colorlight-board_f8084fcc8.html