Carrier Sense Multiple Access with Collision Detect (CMSA/CD) is method to access a network. In CSMA/CD a station listens for traffic before transmitting. If two stations transmit simultaneously, a collision occurs. Collisison detection allows the two stations to detect this event. If a collision is detected, both stations wait a random period of time before attempting to transmit again.
CSMA/CD is used by Ethernet.