Ethernet is a family of wired LAN technologies, standardized as IEEE 802.3, that defines how devices on a local network frame, address, and access a shared or switched medium. Originally based on CSMA/CD (Carrier Sense Multiple Access with Collision Detection) over a shared bus, modern Ethernet mostly runs over switched, full-duplex links where collisions don't occur.

An Ethernet frame includes fields for destination/source MAC address, a type field, the data payload, and a trailing CRC for error detection.

Common cable types used for Ethernet

Cable type	Standard	Typical speed	Notes
Coaxial (Thicknet/Thinnet)	10BASE5 / 10BASE2	10 Mbps	Legacy, bus-topology Ethernet, largely obsolete
Twisted pair (UTP), Cat 5e/6/6a	100BASE-TX, 1000BASE-T, 10GBASE-T	100 Mbps – 10 Gbps	Most common in modern LANs; uses RJ-45 connectors
Fiber optic (single-mode/multi-mode)	1000BASE-SX/LX, 10GBASE-SR/LR	1 Gbps – 100+ Gbps	Used for backbones, long-distance, or high-speed links; immune to EMI

Twisted-pair copper (Cat 5e/6) is by far the most common choice for desktop/office connections today, while fiber is preferred for data-center backbones and long-haul links.