ThickNet, also known as 10BASE5 or IEEE 802.3-1985, is an Ethernet standard that requires a specialized coaxial cable to transmit Ethernet frames at a rate of 10Mbps. It derives its nickname, which is a portmanteau of "Thick Ethernet," from the thick coaxial cable it uses, which is 0.375 inches in diameter.

The designation 10BASE5, assigned to the ThickNet standard by the Institute of Electrical and Electronics Engineers, provides a quick summary of the characteristics of its physical medium: 
"10" denotes its maximum data transmission rate of 10Mbps; 
"BASE" is shorthand for "baseband transmission," meaning the medium exclusively transmits Ethernet signals; and 
"5" means that it can transmit data at a maximum length of 500 meters before it experiences signal degradation.

The specialized coaxial cable used for a ThickNet computer network is sometimes referred to as "yellow cable" or "orange cable" because its outer insulation or jacket is made of either PVC (yellow) or Teflon (orange). This material makes the cable stiff and inflexible.

The cable contains a solid center conductor, and surrounding this conductor is an insulating filler made of foam, as well as a shielding braid. The cable must have a characteristic impedance of 50 ohms. Examples of coaxial cables made specifically for Ethernet include Belden numbers 9880 and 89880. ThickNet may also make use of RG-11 coaxial cable.

ThickNet employs a bus configuration as its network topology, meaning all nodes or devices are connected in a linear manner to one cable, known as a backbone, with 50 ohm resistive terminators at each physical end of the network. No more than 100 nodes may be connected to a ThickNet segment.

Transceivers, also known as Medium Attachment Units (MAU), were widely used in ThickNet networks. The term "transceiver" is a portmanteau of "transmiter" and "receiver," meaning it could both transmit and receive signals.

Transceivers were connected directly to cables through a device known as a "vampire tap," which is called such since it has spikes that pierce directly through the cable’s outer jacket and into its center conductor. An N connector may also be used to connect a transceiver to a cable.

An Attachment Unit Interface (AUI) cable is used to connect a transceiver to a node. Transceivers may only be installed every 2.5 meters in order to not correspond to the wavelength of the signal. This minimizes echo and ensures that the reflections from multiple taps are not in phase.

ThickNet is the original Ethernet specification, although it was quickly superseded by 10BASE2 (also known as "ThinNet"). At present, it is considered obsolete computer networking technology.