A Carrier Sense Multiple Access with Collision Detection (CSMA/CD) network where a collision will occur if two computers attempt to transmit signals at the same time. The larger the collision domain of an Ethernet network, the more computers present and the higher the probability of collisions occurring and negatively affecting network performance.
Collision Domain / Broadcast Domain
If two hubs are connected directly to a third hub, the resulting local area network (LAN) is still only a single collision domain, since only hub connections are used between segments of the network. But if the two hubs are directly connected to an Ethernet switch, you have two collision domains because the switch enables the two networks to function independently.
Bridges and routers can also segment Ethernet networks into smaller collision domains.