Gecekondu (plural gecekondular) is a Turkish word meaning a house put up quickly without proper permissions, a squatter's house, and by extension, a shanty or shack. Gecekondu bölgesi is a neighborhood made of those gecekondular.

In Turkish, gece means "at night" and kondu means "placed" (from the verb konmak, "to settle" or "to be placed"); thus the term gecekondu comes to mean "placed (built) overnight". And bölge means a "zone", "district" or even "region", so a gecekondu bölgesi is a "suddenly built-up shanty-neighborhood."

In common usage, it refers to the low cost apartment buildings or houses that were constructed in a very short time by people migrating from rural areas to the outskirts of the large cities. Robert Neuwirth writes in his book Shadow Cities that these squatters are exploiting a legal loophole which states that if one starts building after dusk and moves into a completed house before dawn the next day without having been noticed by the authorities, then the next day the authorities are not permitted to tear the building down but instead must begin a legal proceeding in court (and thus it is more likely one can stay). Such buildings may be constructed without going through the necessary procedures required for construction, such as acquiring building permits, and can be very densely populated. Neuwirth states that "half the residents of Istanbul - perhaps six million people - dwell in gecekondu homes".