CSMA/CD
On an Ethernet network, before any device can transmit, it must listen to the wire for a carrier signal, which is only present when another station is transmitting.
Listening to the wire is called carrier sense (CS). If no signal is detected, devices can send data.
All devices have equal access to the wire, which is what the multiple access (MA) portion of CSMA/CD describes.
The last part of the name, CD, stands for collision detection, which means that the devices have a way of detecting collisions in the event that two individual transmissions collide on the network.