Definitions for "Broadcast Domain"
Keywords:  subnet, vlan, router, bridges, segment
A broadcast domain is the portion of a network sharing the same layer two network segment. In a network with a single switch, the broadcast domain is that entire switch. In a network with multiple switches interconnected by crossover cables without the use of VLAN's, the broadcast domain includes all of those switches. A single broadcast domain can contain more than one IP subnet, however that is generally not considered good network design. IP subnets should be segregated into separate broadcast domains via the use of separate switches, or VLAN's.
Segments joined together by bridges form a broadcast domain.
Devices sets that receive broadcast frames originating from any device within a designated set. Routers bind Broadcast domains, because routers do not forward broadcast frames.