Tahdiya is Arabic (تهدئة) for "calming" or "quieting".
Tahdiya is a clause in Islam that would permit a Muslim to lie to an enemy (and the Infidel)and even create a peace treaty which he plans to renege on, in the name of Allah. The concept is drawn out from the story of Mohammed and the Bnei Koraish (a Jewish Tribe). They fought a battle but neither side was winning. So they made a treaty, and went back to their encampments. Once the Jews had set aside their weapons and begun to learn the Torah and go to sleep, Mohammed and his followers sneaked in during the night and slaughtered the Jews as they slept.
The term has been applied to a temporary lull between the Israeli forces and the Palestinian Hamas, beginning early in 2004 following the non successful discussions to sign a Hudna, or temporary armistice. While Hudna is a term for temporary armistice, it should not be confused with tadiya, which stands for calming down on hostilities but not a complete stop to them.