what is ballast
ballast - any heavy material used to stabilize a ship or airship. material, stuff - the tangible substance that goes into the makeup of a physical object; coal is a hard black material; wheat is the stuff they use to make bread.
To put it simply, a ballast is the functional heart of a fluorescent or HID light source. Just as a heart regulates blood flow to your body, a ballast ensures that a lamp stays lit by managing the distribution of energy throughout the fixture.