The term Holy Land is a convenient short-hand for Christians (and Crusaders in particular) to refer to Palestine or the Kingdom of Jerusalem, since it is two short words. By being "holy", it implies that the area is invested with a God-given aura (and thereby justifies almost any atrocity committed in its (re-)conquest or defence). It also distinguishes it from the defined lands around it, but this might mean that the Holy Land stretches until one can find another border, which in period would extend it most of the way down Africa, across to India (since the Christians would not have recognised the Muslim rule in Arabia), and north into pagan Russia.
To the Muslims, arguably, the entire Earth is a Holy Land, though the city of Mecca is of particular importance.
When the Crusaders first arrived in the Holy Land, the inland areas were covered by forests. They have since been removed (a considerable amount by Crusaders themselves), and there is a current attempt to re-establish these forests in what was once the Holy Land. Environmentalists are against this.