Förster Resonance Energy Transfer (FRET) is a physical phenomenon where energy is transferred from an excited donor molecule to an acceptor molecule through non-radiative dipole-dipole coupling. This process occurs when the two molecules are in close proximity, typically within 1 to 10 nanometers. FRET is commonly used in biochemistry and molecular biology to study interactions between proteins, nucleic acids, and other biomolecules. FRET efficiency depends on the distance between the donor and acceptor, as well as their spectral overlap. When the donor is excited by light, it can transfer energy to the acceptor, causing the acceptor to emit light at a different wavelength. This property makes FRET a valuable tool for imaging and analyzing molecular interactions in live cells.