Acupuncture (from Latin, acus (needle) and punctura (to puncture)) is a form of alternative or complementary medicine and a key component of Traditional Chinese Medicine (TCM).
Acupuncture is a 5,000 year-old Chinese therapy.  Formerly known as Zhenjiu, it is based on the theory that dysfunction or illness is a result of barriers in the network of meridian pathways that extend throughout the body. These obstructions cause disparities in the flow of vital Qi energy.  Health is maintained when the opposite forces of Yin and Yang are in equilibrium and chi flows without disruption. These channels of energy do not exist in a physical form like the way blood travels through veins, even though some research suggests otherwise. They do, however, exist in a more elusive, vibrational mode.
The best way to visualize meridians is as an energy freeway that traverses through all parts of the human body. Meridians flow in matching pairs with acupuncture points along their pathway. The meridian system is often referred to as an energetic distribution network. Basically, it is best to consider it a process, not a structure.
There are twelve main meridians throughout the body through which Qi (or energy) flows. Each limb is traversed by six channels, three Yin (on the inside), and three Yang (on the outside). Each of the twelve regular channels corresponds to five Yin organs, six Yang organs, the Pericardium, and San Jiao. It is important to remember that these are not western “organs” but relate to processes in the body.
When a meridian has a balanced flow of chi the corresponding organs and body systems will have a better chance of operating optimally. To cultivate this and balance this flow acupuncture points (acupoints) along each of the meridians are activated to dissipate any obstructions by inserting fine needles into them or applying other forms of stimulation.
Acupuncture is one of the fundamental techniques found in traditional Chinese medicine. It is well documented, scientifically analyzed, and widely becoming acceptable in western medicine.