Biofluorescence is essentially the ability of an organism, to absorb electromagnetic wavelengths from the visible light spectrum by fluorescent compounds, and the subsequent emission of this at a lower energy level.
In this blog piece for the BiOME Ecology webzine i talk to plant pathologist James Lynott about this incredible phenomenon: https://biomeecology.com/news/2019/10/shining-a-light-on-shark-biofluorescence-dr-l-smith/