The term 3 PART refers to a type of puzzle called an 'ARC crossword'. It is a type of crossword puzzle that has three parts: the main grid, a set of clues, and a set of answers. The main grid is made up of a series of interconnected arcs, which form a network of words. The clues are written in the arcs, and the answers are placed in the spaces between the arcs. The goal of the puzzle is to fill in the blanks with the correct answers. The challenge of the puzzle lies in finding the correct answers for the clues given.