GFP, or Green Fluorescent Protein, is a protein originally found in the jellyfish Aequorea victoria. It emits a bright green light when exposed to ultraviolet or blue light, making it useful in various scientific applications, particularly in molecular and cellular biology. Researchers use GFP as a marker to visualize and track proteins, cells, and other biological processes in real-time. By attaching GFP to specific proteins, scientists can observe how these proteins behave within living organisms, aiding in the understanding of cellular functions and disease mechanisms.