The coaxial cabling used in standard Ethernet or 10Base5 networking. Thicknet coaxial cabling is usually 3/8 inch in diameter. It is fairly rigid, has an impedance of 50 ohms, and can carry signals up to 500 meters (1640 feet) - hence the designation 10Base5 for «10-Mbps baseband transmission over 500 meters».
To connect a computer to a thicknet cable, you attach a vampire tap to the cable. The tap pierces the cable’s insulation layers and makes contact with the signal-carrying copper core. The tap is connected to a transceiver, and a drop cable connects the transceiver to an AUI connector on the computer’s network interface card (NIC).
Thicknet was commonly used in the 1980s, primarily for Ethernet cabling. It has largely been superseded by twisted-pair and fiber-optic cabling.