The joule is the metric unit of energy, often represented by the abbreviation, "J." The 9th General Congress on Weights and Measures officially defined it in 1948 as "the work done when the point of application of 1 newton moves a distance of 1 meter in the direction of the force." In other words, it is the energy it takes for you to move an object one meter using one newton of force. Because work is another term for the transfer of energy, the joule is also used as the unit of work.
The joule was named after James Joule, whose experiments proving the relationship between work and heat energy influenced the scientific community towards further developments in the field of energy. The joule was adopted as the unit of electrical energy in 1889 by the International Electrical Congress in Paris; the unit of heat, energy and electrical and mechanical work in 1948 by the General Conference on Weight and Measures; and a derivative unit equal to one newton-meter in the metric, or International System (SI) in 1960.
Because energy is an integral part of existence, people perform functions that a scientist would measure in joules every day. For instance, when you walk into your kitchen in the morning and turn on the light, joules measure the amount of energy used by the light bulb. When you make a bowl of oatmeal, it measures the amount of energy required to heat the water. And when you pour yourself a glass of milk, it measures how much energy it took to lift the gallon.
One joule equals one newton-meter (N*m) or one square meter-kilogram per square second (k*m^2/s^2). It is also equal to the energy used by one ampere of current traveling through one ohm of resistance in one second. When referring to heat energy, 4.2 joules is the amount of energy needed to raise one gram of water one degree Celsius. In the centimeter-gram-second system, where the erg is the standard unit of energy, 10,000,000 joules equal 1 erg.