Tri-phasic cloning was a cloning technique. Clones created using this method had a characteristic gene-sequence degradation.
In 2369, Ibudan used this method to clone himself in order to frame Odo for his own murder. Ibudan had learned about tri-phasic cloning while incarcerated at Kran-Tobal prison from a fellow Bajoran inmate who was a geneticist. (DS9: "A Man Alone")