ThinNet, also known as 10BASE2, IEEE 802.3, or "CheaperNet," is an early Ethernet standard that makes use of industry-standard RG-58 coaxial communications cables connected to BNC T-connectors. The standard has been nicknamed as such due to the thin and relatively inexpensive coaxial cables or "thinwire" used, which are 5 millimeters (0.2 inches) in diameter; "ThinNet" is a portmanteau of "Thin Ethernet."

The Institute of Electrical and Electronics Engineers (IEEE) has assigned ThinNet the identifier 10BASE2, as a quick summary on the following characteristics of the standards:

• "10" means it has a maximum transmission speed of 10Mbps;
• "BASE" is shorthand for "baseband transmission" or "baseband Ethernet," meaning that the medium only transmits Ethernet signals; and
• "2" refers to its maximum network segment length of 185 meters, rounded up to 200 meters.

Aside from its maximum segment length, it is of note that there is also a minimum length for this standard. Cables must not be any shorter than 0.5 meters. Other restrictions for ThinNet include: no more than 30 devices may be attached to a single ThinNet port per segment or "daisy chain"; no more than 3 repeater devices may be used to connect two network devices; and a maximum of 5 connected segments are allowed.

BNC T-connectors are used to connect each cable segment to a Medium Attachment Unit (MAU), LAN card or transceiver, which is then connected to the computer. In terms of network topology, a ThinNet network is usually arranged in a bus configuration, meaning each computer station or node is attached to the cable segment, which is ended by a terminator on either side to prevent interference caused by a radio frequency signal from being reflected back from the end. RG-58 coaxial cables have a nominal impedance of 50 Ohms, so 50 Ohm terminators are required for termination at the physical end of a network.

It is important to assure that everything in a ThinNet network is properly installed and connected, because connection flaws at any point of the network cabling tend to prevent all communications, and it very difficult to diagnose bad contacts or shorts (although a time-domain reflectometer may aid in finding problems).

Wall-mounted EAD-sockets can, however, provide more reliable connections. In this aspect, 10BASE-T networks are preferable because they are easier to maintain, but ThinNet does have a number of advantages over 10BASE-T: it has cheaper hardware costs, and wiring is easier since only a single wire run is needed. Thus, ThinNet is more ideal for smaller networks, while 10BASE5 or 10BASE-T are preferable options for larger networks.

Among 10Mbps Ethernet standards, ThinNet was the most popular for several years, widely used for home desktop machines, but it has since been superseded by standards featuring the low-cost Category 5 cable, wireless local area network (WLAN) standards, and Ethernet standards featuring much faster transmission rates (i.e. 100Mbps or higher). In present-day computer networking, ThinNet is considered obsolete technology.