Editing Wave (section)

=== Absorption ===
{{Main|Absorption (acoustics)|Absorption (electromagnetic radiation)}}
Waves are usually defined in media which allow most or all of a wave's energy to propagate without [[Insertion loss|loss]]. However materials may be characterized as "lossy" if they remove energy from a wave, usually converting it into heat. This is termed "absorption." A material which absorbs a wave's energy, either in transmission or reflection, is characterized by a [[refractive index]] which is [[Complex number|complex]]. The amount of absorption will generally depend on the frequency (wavelength) of the wave, which, for instance, explains why objects may appear colored.