Sinus Meridiani is a classic albedo feature on Mars stretching east-west just south of that planet's equator. The area was named by the French astronomer Camille Flammarion in the late 1870s when he worked on his compilation and analysis of all prior observations of Mars.

Prior astronomers, notably the German team of Wilhelm Beer and Johann Heinrich Mädler and then the Italian Giovanni Schiaparelli, had chosen a particular point on Mars as being the location of its prime meridian when they charted their observations. Accepting suggestions that dark areas on the surface of Mars were seas or oceans, Flammarion named a dark area at that point "Sinus Meridiani", literally "Meridian Bay".

Since flyby and orbital spacecraft imagery of Mars began to become available in the 1960s, dark-light albedo features on the planet have seen shifting of names to more accurately reflect the nature of the topography. Sinus Meridiani consequently became also known as Terra Meridiani, or "Meridian Land", or as Meridiani Planum, the "Meridian Plateau". However, some texts will distinguish that Meridiani Planum, now much popularized as the landing place of Mars Exploration Rover Opportunity, lies in the western portion of Sinus Meridiani.