Lead (Pb) is a dense metallic chemical element with atomic number 82. Lead's symbol Pb comes from its Latin name, plumbum. There are several stable lead isotopes, but the most abundant one is 208Pb, with 82 protons and 126 neutrons.
Lead is a soft but very dense metal. It has a long history of being used for bullets, for several reasons. Firstly because it's cheap, allowing for mass production, and also because it's heavy meaning the bullets retain their velocity. Thirdly, since lead has a low melting point it can be easily cast to the right bullet shape. Even today, lead is used in bullets, although alloyed with other metals to make them harder.
Lead has been known to Man since thousands of years, and has had various applications over that time. However, in modern society lead is increasingly being replaced and phased out due to its toxicity.