The Accelerated Graphics Port (often shortened to AGP) is a high-speed point-to-point channel for attaching a video card to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics. Originally it was designed as a successor to PCI type connections. Since 2004 AGP has been progressively phased out in favor of PCI Express (PCIe). By mid-2009 PCIe cards dominated the market; AGP cards and motherboards were still produced, but OEM driver support was minimal.
Read more about AGP: Advantages Over PCI, History, Versions, Compatibility, Power Consumption, Legacy Use