a protein produced by a jellyfish Aequorea victoria which fluoresces in the lower green portion of the visible spectrum when exposed to blue light. GFP has become an invaluable tool in contemporary cell and molecular biology research, because its intrinsic fluorescence can be visualized in living cells. GFP has become well established as a marker of gene expression and protein targeting in intact cells and organisms. Mutagenesis and engineering of GFP into chimeric proteins are opening new vistas in physiological indicators, biosensors, and photochemical memories

A protein found in a jellyfish that fluoresces, or glows green, when UV light shines on it. GFP can function as a biological marker when attached to other proteins. The structure of the protein is cylindrical with the glowing component, an amino acid complex called a fluorophore, in the middle.

A protein naturally occurring in some animals including jelly fish that spontaneously fluoresces. It can be used as a noninvasive marker in living cells by attaching it to different proteins and then letting it fluoresce so as to track the cell.