<networking, hardware> The original "full spec" cable used for 10base5 Ethernet networks. RG8 is stiff, large diameter coaxial cable with an impedance of 50 ohms, a member of the "Radio Guide" series. The outer sheath is usually yellow, to indicate double shielding, so it is often just called "yellow cable".
10base5 cable is designed to allow transceivers to be added while existing connections are live. This is achieved using a "vampire tap".
RG8 is sometimes called "thicknet" or "thick Ethernet" in contrast to RG58, a cheaper, thinner, more flexible alternative.