This is an algorithm (implemented in the network-card hardware)
which defines how computers using Ethernet/802.3 can efficiently
share a common medium: Carrier Sense, Multiple Access, with
Collision Detection.
Multiple Access
All computers have equal access: there are no masters or
slaves, etc. If the shared channel is clear (ie, not in use), a
computer may begin to transmit immediately.
Carrier Sense
If the channel is busy, continue to "listen", and attempt to
transmit as soon as it becomes available.
Collision Detection
If a collision is detected (ie, another
computer started to transmit at the same time, so the signal is
garbled), immediately cease transmission. Wait a random period of
time, then start all over.