A gigajoule (GJ) is a unit of energy measurement in the International System of Units (SI). It is equal to one billion joules, where a joule is the energy transferred when one newton of force moves an object one meter. Gigajoules are commonly used to quantify energy in various fields, including electricity, heating, and fuel consumption. In practical terms, a gigajoule can represent the energy needed to power a household for several days or the energy content of about 26 liters of gasoline. Understanding gigajoules helps in comparing energy sources and managing energy consumption effectively in contexts like renewable energy and energy efficiency.