RG-58/U is a type of coaxial cable often used for low-power signal and RF connections.
"RG" was originally a unit indicator for bulk RF cable in the U.S. military's Joint Electronics Type Designation System.
There are several versions covering the differences in core material (solid or braided wire) and shield (70% to 95% coverage).
RG-58 cable is often used as a generic carrier of signals in laboratories, combined with BNC connectors that are common on test and measurement equipment such as oscilloscopes.
RG-58 in versions RG-58A/U or RG-58C/U was once widely used in "thin" Ethernet (10BASE2), for which it provides a maximum segment length of 185 meters.