The Terrace Farm is a unique tile improvement of the Incan civilization in Civilization VI: Gathering Storm. It is available without any technological research and must be built on Grassland Hills, Plains Hills, or Desert Hills tiles. It can also be built on Volcanic Soil (regardless of its relief).
Terrace Farms, if employed correctly, can give an enormous early game boost to the Incan player. They will significantly boost Food production, while also increasing Production yields, which are the two yields every single city can benefit from!
Make sure to place your Terrace Farms next to Mountains and, if possible, Rivers, Lakes, or Aqueducts to gain the greatest Food and Production yields possible. This will give you both populous and productive cities, and many Terrace Farms will provide you with Housing to support the enormous Population that your cities might have if situated near Mountains.
Note that Terrace Farms also enjoy adjacency bonuses with Feudalism and later with Replaceable Parts; however, these are triggered only by other Terrace Farms, not normal Farms. Also, Terrace Farms don't provide adjacency bonuses to normal Farms, nor can they unlock the Inspiration for Feudalism (either alone or in combination with normal Farms).
The Incan terrace farm is one of the most sophisticated engineering works and agricultural systems developed in South America, and one whose complexities and benefits have only recently come into fuller appreciation. The Inca created arable land in a dry mountain region, capable of supporting a variety of crops and animals, and linked together to make optimal use of scarce resources and microclimate variations.
Terrace farms have extensive irrigation canals and cisterns to move water to needed locations. The terraces provide level ground to grow crops, and the stone walls help preserve the day's heat and transfer it back to the soil at night, which mitigates crop freezing. Higher elevations were used as pastoral land for the llamas and alpacas, and different crops planted at different elevations, with the hardier crops like potatoes being raised higher. Each terrace was well-drained, and the water would flow down to help irrigate the terrace below. Lower terraces could be used to raise beans, peppers, and various gourds. The system of terrace farming produced enough surplus food that the Incas created and maintained caches of food for times of drought or disaster.
In recent years, archaeologists and indigenous Andean communities have begun work to understand the terrace farms in the context of this agricultural system. They are rehabilitating some terraces and reintroducing some of the terrace farming techniques their Incan ancestors pioneered in order to feed a growing South American population.