The Wright brothers launched the 1903 Flyer from a wooden monorail at Kitty Hawk.
Because the sandy ground was unsuitable for wheels and the aircraft had no conventional landing gear, the Flyer rested on a small wheeled launching carriage. The carriage ran along a straight wooden rail as the engine accelerated the airplane into the wind.
The rail was about 60 feet long and was positioned into the prevailing wind. The arrangement allowed the Flyer to reach flying speed over a short distance without requiring a paved runway.
This launch system is sometimes called a track or launching rail, but “monorail” is the standard concise description. It should not be confused with a catapult: the aircraft was accelerated by its own engine, not thrown into the air by an external mechanism.