A retaining wall is a stabilizing structure used to hold sloping ground in place and to prevent the erosion and the movement of soil. It is normally designed with seepage.holes (called weep holes - as water seeps from them and they seem to be weeping), which allow collected ground water to escape. This releases the additional water pressure, created by accumulated water and helps keep the retaining wall stable.
Retaining walls can also be designed to hold back water, not just sloping ground or soil. It may also serve to retain other materials, such as in a go-down or storage rooms.