Collier's Entrance is a term used to describe the entrance of a mine or tunnel. It is also known as an ADIT, which is a four-letter word that is often used in crosswords. An ADIT is an entrance to a mine or tunnel that is usually horizontal and has been dug into the side of a hill or mountain. It is used to provide access to the underground workings of a mine or tunnel. The term Collier's Entrance is derived from the fact that it was originally used by coal miners, or colliers, to access the coal seams.