• Energy efficiency, useful work per quantity of energy
  • Energy conversion efficiency, desired energy output per energy input
  • Energy conservation, reducing the use of energy
  • Electrical efficiency, useful power output per electrical power consumed
  • Fuel efficiency, converting energy in fuel to kinetic energy or work
    • Specific impulse, in propulsion systems, a measure of fuel-efficiency
  • Volumetric efficiency, in internal combustion engine design
  • Lighting efficiency, visible light from a light source per unit of energy, in lumens per watt
  • Mechanical efficiency, the effectiveness of a simple machine, mechanical advantage over ideal mechanical advantage
  • Thermodynamic efficiency, useful work per change in heat
    • Exergy efficiency, measure of 2nd-law themodynamic loss
    • Thermal efficiency, useful work per the higher heating value of the fuel
  • Radiation efficiency, ratio of radiated power to power absorbed at the terminals of an antenna
• Efficiency (aerodynamics), for fixed wing aircraft the Lift-to-drag ratio
• Efficiency (economics), a general term, to capture the amount of waste or other undesirable features
  • Pareto efficiency, making one individual better off, without making any other individual worse off
  • Kaldor-Hicks efficiency, like a less stringent Pareto efficiency
  • Allocative efficiency, an optimal distribution of goods
  • The optimisation of a social welfare function
  • Efficiency wages, paying workers more than the market rate for increased productivity
• Efficiency (statistics), a measure of desirability of an estimator
• Efficiency ratio, expenses as a percentage of revenue, etc.
• Efficiency Movement, of the Progressive Era 1890-1932, advocated efficiency in the economy, society and government
• Material efficiency, compares material requirements between construction projects or physical processes
• Faraday Efficiency, electrolysis
• Textual efficiency, density of a message
• Algorithmic efficiency, the speed and space requirements of a computer program
• Quantum efficiency, a measure of sensitivity of a photosensitive device: the percentage of photons hitting the photoreactive surface that will produce an electron–hole pair
• Efficient (horse), winner of the 2007 Melbourne Cup.
• Efficiency apartment, a one room apartment, also called a Studio apartment

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