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Electromagnetic Waves

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.
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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.
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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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