From what I saw in the Wikipedia entry (I know people don't consider Wikipedia a reliable source here, but it's the best I could find on the subject) it's only mentioned once in the old testament as the "holy land" and usually referred to as "promised land".
So where does the habit referring to the location as "holy land" comes from? When/How the habit of calling it the "holy land" originated? Who were the first people to commonly refer to it as the "holy land" and why?
EDIT: I'm sorry if didn't phrase my question properly. I didn't mean to ask why people call it the "holy land", but when/how the habit of calling it the "holy land" originated?
This area of the world has a lot of different names, and all of them have different connotations.
The term "Holy Land" comes from the region's role as a central point in three major world religions, Judaism, Islam, and Christianity. Jerusalem is a holy city for all three religions. Judaism and Christianity began there, and the Dome of the Rock sits on the ancient Jewish Temple Mount.
So it's called the Holy Land because it has a lot of religious connotations.