What is an em wave?

Answer 1

It is an "electromagnetic wave."

Electromagnetic waves are by definition is any kind of actual radiation. X-Ray, microwaves, light, radio waves, and gamma rays. It does not include those forms of matter more commonly known as radiation (alpha and beta particles), or neutrinos.

An EM wave is actually a combination of both electric and magnetic fields, perpendicular to each other and to the direction of propagation of the wave.

Answer 2

The wave , which do not require medium for their propagation i.e., which can propagate even though the vacuum are called electromagnetic wave. They propagates as transverse waves.

Answer 3

Electromagnet