A joule (J) is a unit of energy in the International System of Units (SI). It measures the amount of energy transferred when a force of one newton moves an object one meter. Joules can also represent other forms of energy, such as heat or electrical energy, making it a versatile unit in physics. In practical terms, one joule is equivalent to the energy required to lift a small apple (about 100 grams) one meter against the force of gravity. Understanding joules helps in various fields, including mechanics, thermodynamics, and electrical engineering.