Acupuncture points (also called "acupoints or tsubo") are specific anatomical locations on the body that are believed to be therapeutically useful for acupuncture, acupressure, sonopuncture, or laser treatment. Medical science does not currently understand how these points work, but cheap commercial devices can detect changes in the electrical conductivity of the skin at these points. Most of the research into acupuncture mechanisms is taking place in China.
Acupuncture points are usually located by palpation of the local region, often by locating a depression on the body that can be felt with the finger. Many acupoints are also located by a measurement technique that is calibrated according to proportion. Acupoint location usually depends on specific anatomical landmarks that can be palpated. Trigger points are usually acupoints that are located exclusively by tenderness, with a bit of pressure. Location by tenderness is also a common way of locating acupoints. Acupoint location can be difficult to learn, but gets easier with practice. There are nearly 400 basic acupoints on the meridians. Many of these basic points are rarely used. Some points are considered more therapeutically valuable than others, and are used very frequently for a wide array of health conditions.
Additionally, there are microsystems of acupoints that are typically not located on the meridians. For example, auriculotherapy uses the external ear microsystem exclusively, utilizing thousands of points that are not on a meridian, but located on the surface of the external ear. The Korean system of hand acupuncture is a microsystem that utilizes acupoints on the hand. There are other common and uncommon acupoints that are called extra points, meaning that they are neither on a meridian nor part of a microsystem.
Basic acupoints are referred to either by their traditional name, or by the name of the meridian on which they are located, followed by a number to indicate what order the point is in on the meridian. A common point on the hand, for example, is named Hegu, and referred to as LI 4 which means that it is the fourth point on the Large Intestine meridian. Extra points are referred to more often by name, though some of the more commonly known have a letter/number combination for reference. A popular extra point is Yintang, located at the midpoint between the eyebrows.