Abbreviated CNR, it is a riser specification from Intel for dedicated connection of high-speed network adapters. It was designed to address many of the shortcomings of it's predecessor, the AMR slot, and to provide higher speed for emerging communications technologies.
CNR is a card edge connector that is similar in length and design to PCI, though it is keyed differently and is usually placed slightly closer to the backplane of the motherboard than PCI expansion slots. In fact, the CNR slot is a PCI slot, simply installed backwards.
The CNR specification supports five logical interfaces: Audio Codec '97 (AC'97, for audio output and modem functions), Universal Serial Bus (USB, serial peripheral interface), System Management Bus (SMBus, provides the Plug and Play functionality), LAN Connect Interface (LCI, for ethernet or PNI/HPN connections) and Media Independent Interface (MII, also for ethernet or PNI/HPN). Up to two AC'97 interfaces, one communications interface and an SMBus interface can be used with one CNR logic controller. This makes perfect sense as is allows a sound card and modem (via the AC'97 interface) and LAN (via LCI or MII) on one connector.
The CNR specification was designed to also support AMR devices, though many AMR devices do not actually properly support the AMR implementation, so use of an AMR device with a CNR interface is discouraged unless the device is specifically noted as having CNR slot compatibility.