1. Procedures that weaken an agent of disease (a pathogen): "An attenuation of a virus is a weakened, less vigorous virus."

"A vaccine against a viral disease can be made from an attenuation, a less virulent strain of the virus, a virus capable of stimulating an immune response and creating immunity but not causing illness."

2. In physics, a reduction in amplitude, density, or energy resulting from friction, absorption, or scattering.
3. A loss of solar irradiance as it passes through the atmosphere to the surface of the earth.
4. A reduction in the toxicity of a pollutant substance in the environment; especially, as a result of natural processes: "The attenuations of bacteria and viruses are made less virulent by being heated, dried, treated with chemicals, passed through another organism, or cultured under unfavorable conditions."

"Attenuated bacteria are often used as vaccine agents."

5. The process of reduction: "There is an attenuation of an x-ray beam when its intensity is reduced."
6. The reduction of amplitude, magnitude, or strength of an electrical signal: "In electronics, an attenuation is the opposite of an amplification."

The depletion of electromagnetic energy in the layers of gases surrounding the surface of the Earth because of absorptions or diffusions: The astronomers discovered that the rate of the atmospheric attenuation of the electric sound waves had decreased when passing through dense clouds.

In radiography, or ultrasound, the difference between the energy that enters a body part and the energy that is not detected: "The differences that occur with attenuation coefficients are caused by the absorption and scattering of energy within the body tissues."

The weakening of RF energy from an RFID tag or reader.

Water absorbs UHF energy, causing signal attenuation.

In electromagnetism, attenuation over an imperfectly conducting spherical earth in excess of that over a perfectly conducting plane.

The term attenuation refers to the reduction with distance from the source of the intensity of an electromagnetic signal propagating through the atmosphere caused by the interaction of the signal with gaseous constituents of the atmosphere, aerosols, or hydrometeors.

It also includes the reduction of intensity of a radiation as it passes through a medium and it includes reductions due to both absorption and scattering.

The ratio of the magnitude of the voltage across the input of a transducer to the magnitude of the voltage delivered to a specified load impedance connected to the transducer.

It is expressed in decibels by multiplying the common logarithm of the ratio by 20.