The oche also known as the throw line or toe line, in the game of darts is the line behind which the throwing player must stand. For steel tipped darts, it is generally 7 ft 9 1⁄4 in (2.36855 m) from the face of the dartboard, measured horizontally. This is the recognized world standard as set by the World Darts Federation and is used in most areas.

The throwing player must stand so that no portion of either foot extends past the edge of the oche closest to the dartboard. One or both feet may touch any other portion, and the player may lean forward over the oche if desired. In decent darts venues the oche will be a raised board so that a throwing player can't overstep the line. All measurements should be to the foot of the oche board.

The origin of the term oche is unknown, though it probably came into use in the 1920s. It was originally spelled "hockey", only becoming "oche" in the late 1970s.

More Info: en.wikipedia.org