Today, a small region east of Israel. Before May 1948 it included the territory that is now Israel as well and was under British control. Before the end of WW 1 in 1918 it belonged to Ottoman Empire under Turkish rule since 1516.
Palestine is the holy land of Muslims. It was "given" to the Jews after WWII as a "sorry" for all of their people being killed. Jerusalem is where Palestine is and Jews control it but the Muslims want it back and blah blah