Rigging is usually used to refer to hanging the required gear from the required bars. For example, rigging a light is usually meant to refer to hanging the light off the required bar.
A greater scope of rigging also includes adding the power cables and dmx/control cables to the fixture, the bracket that attaches to the lighting fixtures to hang it from, safety cables as well as the actual structure of what the lights hang from (trussing).
Most of the larger touring rigs are created using aluminimum tubing truss sections, usually 4 lengths of 50mm diameter aluminimum tubing with smaller 20mm diameter tubing braces at regular intervals along the length and is formed in a square pattern of a 290mm x 290mm width and height and of various length from 500mm to 3m+. This is called 4 point trussing. See picture below of a typical 4 point trussing section, you can see the main tubing and the braces and at the end the machined section which will take the connector and the pin..
Along with the straight sections of truss there are also corners of every conceivable type, for example 90° left or right with a 90° down as well, t-sections, even ones that go off in every direction at 90° from each other, so you have up, down, left, right, back and front. They also come in other angles such as 135° and in curved sections which can be connected together to produce a circle. They connect with each other using machined aluminimum connectors that are held in place by steel pins. Below is a picture of some other 4 Point Truss Sections.
Aluminimum trussing is available in 3 point and 2 point sections. Trussing can also be made from steel