Unlike conduction and convection, radiation can occur without the presence of matter and a thermal gradient.
E is a ratio that describes how well a surface emits radiation compared to a perfect emitter.
B is the Stefan-Bolztmann constant and characterizes radiation from a perfect emitter. The electromagnetic spectrum characterizes radiation as a wave. It is described by its frequency and wavelength. The frequency tells how many waves pass by a fixed point in a given amount of time. The wavelength is the distance from crest to crest of the wave.