Wiktionary
n. A well or pond in which the water can be reached by descending a set of steps
Wikipedia
Stepwells are wells or ponds in which the water may be reached by descending a set of steps. They may be covered and protected and are often of architectural significance. They also may be multi-storied having a bullock which may turn the water wheel ("rehat") to raise the water in the well to the first or second floor.
They are most common in western India. They may be also found in the other more arid regions of South Asia, extending into Pakistan. The construction may be utilitarian, but sometimes includes significant architectural embellishments.
All forms of the stepwell are examples of the many types of storage and irrigation tanks that were developed in India, mainly to cope with seasonal fluctuations in water availability. A basic difference between stepwells on the one hand, and tanks and wells on the other, was to make it easier for people to reach the ground water, and to maintain and manage the well.
In some related types of structure (johara wells), ramps were built to allow cattle to reach the water.
The builders dug deep trenches into the earth for dependable, year-round groundwater. They lined the walls of these trenches with blocks of stone, without mortar, and created stairs leading down to the water. The majority of surviving stepwells originally also served a leisure purpose, as well as providing water. This was because the base of the well provided relief from daytime heat, and more of such relief could be obtained if the well was covered. Stepwells also served as a place for social gatherings and religious ceremonies. Usually, women were more associated with these wells because they were the ones who collected the water. Also, it was they who prayed and offered gifts to the goddess of the well for her blessings. This led to the building of some significant ornamental and architectural features, often associated with dwellings and in urban areas. It also ensured their survival as monuments.
Stepwells usually consist of two parts: a vertical shaft from which water is drawn and the surrounding inclined subterranean passageways, chambers and steps which provide access to the well. The galleries and chambers surrounding these wells were often carved profusely with elaborate detail and became cool, quiet retreats during the hot summers.