Rare metals are metals that are less abundant in the earth crust, sparsely distributed or difficult to extract from raw materials, such as lithium, beryllium, titanium, vanadium, germanium, niobium, molybdenum, cesium, lanthanum, tungsten, radium, etc. According to their physical and chemical properties and different production methods can be divided into: (1) rare light metals, such as beryllium, lithium, rubidium, cesium, etc.; (2) rare precious metals, such as platinum, iridium, osmium, etc.; (3) rare dispersed metals, such as gallium, germanium, indium, thallium, etc.; (4) rare earth metals, such as scandium, yttrium, lanthanum, cerium, neodymium, etc.; (5) refractory rare metals, such as titanium, zirconium, tantalum, vanadium, niobium, etc.; (6) radioactive rare metals (6) radioactive rare metals, such as polonium, radium, actinium, uranium, plutonium, etc. Rare metals are mainly used in the manufacture of special steels, super-hard alloys and high-temperature resistant alloys in the electrical industry, chemical industry, ceramic industry, atomic energy industry and rocket technology, etc.

     With the extensive research on rare metals, the discovery of new sources and new refining methods, and the expansion of their applications, the boundaries between rare metals and other metals will gradually disappear, such as some rare metals are more abundant in the earth's crust than copper, mercury, cadmium, and other metals. Some rare metals have similar physical-chemical properties and are not easy to be separated into single metals. In the 19th century, the term "rare elements" was introduced, and in the 1920s, it was named as rare metals on this basis. Rare metals are sometimes called new metals because of their late development. Since the Second World War, due to the development of new technologies and increased demand, the research and application of rare metals has developed rapidly, new metallurgical processes have emerged, and the production of these metals has gradually increased. Rare metals are no longer rare. The metals included in rare metals are also changing, for example, titanium is increasingly used in modern technology and production has increased, so it is sometimes included in light metals.