The term 'Great Gulf' is a reference to the Grand Canyon, which is an immense canyon located in Arizona, USA. It is one of the most iconic natural wonders of the world and is known for its vast size and depth. The crossword solution for this term is 'ABYSS', which is a deep chasm or gorge, usually filled with water. This accurately describes the Grand Canyon, which is a deep and wide chasm that was carved out by the Colorado River over millions of years.