What is the ellipse in Washington d.c.?

The Ellipse is a 52-acre (21 ha) park in the National Mall in Washington, D.C. Situated between Constitution Avenue and the Reflecting Pool, it stretches from 15th Street NW to 23rd Street NW. The Ellipse is bounded by the Washington Monument to the west, the World War II Memorial to the east, and the Lincoln Memorial to the south.