Harad was divided in Near and Far Harad, and did not form a union: there were many Haradrim tribes, many of them hostile to eachother. But during the Third Age the Men of Near Harad fell under the influence of Mordor, and became a peril for Gondor.
Much of Far Harad was a jungle, although there also was a desert. In Far Harad lived the huge mammoth-like animals known as Oliphaunts, which were used by the Haradrim as moving war towers.
Near Harad later formed a union with the Corsairs of Umbar, and it was in a series of continual battles with Gondor over South Gondor or Harondor. Anciently its northern border was held to be the river Harnen, but by the time of the War of the Ring all the land south of the river Poros was under Haradrim influence.
To the east of Near Harad lay the land of Khand.