The interaction between the electronic excited states of two dye molecules. The excitation is transferred from one (the donor) dye molecule to the other (the acceptor) dye molecule. FRET is distance-dependent and occurs when the donor and the acceptor dye are in close proximity (6 to 10 nucleotides). This is why chemistries that allow for shorter probes (like MGB or LNA probes) increase the detection sensitivity of the target.