10BASE2, or IEEE 802.3, is an early Ethernet Standard that makes use of industry-standard RG-58 coaxial communications cables connected to BNC T-connectors.

10BASE2 gets its identifier, assigned by the Institute of Electrical and Electronics engineers (IEEE), from the following characteristics: "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.

Due to the thin and relatively inexpensive coaxial cables or "thinwire" used, which are 5 millimeters (0.2 inches) in diameter, 10BASE2 may also be referred to as "thinnet" (a portmanteau of "thin Ethernet") or "cheapernet."

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 10BASE2 include: no more than 30 devices may be attached to a single 10BASE2 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 10BASE2 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 10BASE2 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 10BASE2 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. This makes 10BASE2 more ideal for smaller networks, while for larger networks, 10BASE5 or 10BASE-T are preferable.

Among 10Mbps Ethernet standards, 10BASE2 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, 10BASE2 is considered obsolete technology.