Electromagnetic waves are transverse, but they are not mechanical. They do not require a medium.
The fact that they are not mechanical means that electromagnetic waves can transport energy in a vacuum. As we know from everyday experience, light or electromagnetic waves can also travel in media such as air, water, and glass.
Electromagnetic waves consist of oscillating electric and magnetic fields.
As with mechanical waves, electromagnetic waves carry energy (proportional to the square of the amplitude of the electric and magnetic fields) and have a wavelength and a speed.
The speed of electromagnetic waves in vacuum is always c, the speed of light ( `3 x 10^8` meters per second). In other media, the speed is less than c.