A petajoule (PJ) is a unit of energy in the International System of Units (SI). It is equal to one quadrillion joules, or 10^15 joules. This measurement is often used in fields like physics, engineering, and energy production to quantify large amounts of energy, such as that produced by power plants or consumed by cities. To put it in perspective, a petajoule is equivalent to the energy released by burning about 25 million liters of gasoline. It helps in understanding energy consumption and production on a large scale, making it a crucial concept in discussions about renewable energy, fossil fuels, and climate change.