Electromagnetic radiation is also called electromagnetic waves because the phenomena has a defined frequency for its oscillations.
Electromagnetic radiation requires no medium for the propagation of its fields.
Aether was proposed for the medium ( even back in ancient times just to fill space) but was never detected.
Here is wikipedia's description of how electromagnetic radiation works.
Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light, which, in a vacuum, is commonly denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The wavefront of electromagnetic waves emitted from a point source (such as a light bulb) is a sphere. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength.
Simple explanation: EM radiation is synchronized electromagnetic fields.
The explanation mentions 'homogeneous, isotropic media' which also applies to outer space, which is essentially no media.
Electric fields and magnetic fields do not require a medium.
Electromagnetic radiation does not require a medium.
If the EM is in a physical medium, not a vacuum, then its behaviors can change, including its speed.
from online source:
light waves passing by matter are affected by matter: slowed down, bent, absorbed, maybe even distorted into other frequencies of wave.
Sound waves require a medium because it requires a physical oscillation of matter. EM radiation uses electromagnetic fields which do not require matter.
Light does not require a medium.
link with an illustration of the fields.
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