Beryllium is a chemical element with the symbol Be and atomic number 4. It is a hard, greyish-white metal that is very lightweight and has a high melting point. Beryllium is used in a variety of industries, including aerospace, automotive, defense, and electronics, because it is strong, lightweight, and has good thermal conductivity. However, beryllium dust or fumes can be toxic, leading to respiratory and skin problems for those who are exposed to it.