Carrier Sense Multiple Access / Collision Avoidance - a set of rules that determine how some network devices respond when two devices attempt to use a data channel simultaneously (called a collision). Standard Ethernet networks use a more efficient counterpart to this called CSMA/CD.

The standard puts a warning signal on the channel before using it in order to let other devices know that the channel will be in use. This allows the others to avoid a collision by not transmitting on the line.