PBM is short for Photobiomodulation. It merely means the stimulation of body cells using low-level light. It embodies its ideology in phototherapy and stimulates the body by acting on light sensors such as chromophores and triggers various processes within the body.
PBM is all about the body, how it reacts to light, and the processes that are triggered by it. PBM is being talked about whenever you hear of low-level light therapy.