Israel has reportedly used white phosphorus near Lebanese cities and towns. What is it?

A piece of alleged white phosphorus still burns at UNRWA's (UN Relief and Works Agency) primary school in Beit Lahia in the northern Gaza Strip on January 24, 2009. Oliver Laban-Mattei/AFP hide caption toggle caption Oliver Laban-Mattei/AFP Human rights groups and The New York Times say they have documented Israel's use of the chemical white phosphorus over civilian areas in Lebanon. It is a substance that can cause severe burns, respiratory issues and death. …