1. A long and open portico (a porch or walkway with a roof supported by columns, often leading to the entrance of a building) for athletic exercises in Greek and Roman antiquity: The Xystus of Elis was a famous gymnasium consisting of a large enclosure surrounded by a wall.

The gymnasium was the largest xystus in ancient Greece because all of the athletes in the Olympic games were required to undergo a month of training there before the opening of the games.

Within the xystus, there were special places for runners which were separated from each other by trees.

2. Etymology: a reference to "a polished course" or "a race"; "to scrape, to scratch, to polish"; so called indirectly to the polished floor of the portico or ancient structure consisting of a roof and supported by columns with no walls.