B
B channel	Bearer channel. DS0 time slot that carries analog voice or digital data over ISDN. In ISDN, a full-duplex, 64-kbps channel used to send user data. See also D channel.
backhaul	Process in which telephony signaling is passed from a gateway to a an external media-gateway controller for processing.
backplane	Physical connection between an interface processor or card and the data buses and the power distribution buses inside a chassis.
BER	Bit error rate. Ratio of received bits that contain errors to the total number of transmitted bits.
BGW	Business gateway.
bind	In SIP and MGCP, configuring the source address for signaling and media packets to the IP address of a specific interface.
BITS	Building integrated timing supply. Master timing supply for a building. Also known as a synchronization supply unit.
blind transfer	Call transfer in which the transferring phone connects the caller to a destination line before ringback begins. For example, an auto-attendant uses blind transfer to redirect calls when it receives an extension number.
BOC	Bell operating company.
branch	A fork consists of multiple media streams. Each of these streams is referred to as a branch.
BRI	Basic Rate Interface. ISDN interface composed of two B channels and one D channel for circuit-switched communication of voice, video, and data. See also ISDN Protocol and PRI.
BRQ message	Bandwidth-Request RAS message.
business gateway	xGCP media gateway. Business customer-premises equipment that connects to the VoIP network and to a user's telephony equipment (typically a PBX, corporate LAN, or WAN). Such gateways are used to eliminate or reduce the need for individual medium (voice, data, and so forth) connectivity.
buttons	Physical keys on an IP phone other than those in the numbered keypad. Phone buttons are of two types: line buttons and function buttons. Line buttons can be used for extensions (ephone-dns) or for speed-dial numbers. Function buttons perform specific actions; examples are Volume, Mute, Services, Directories, and Navigation buttons. See also soft keys.

Source: www.cisco.com