The concept of planting different crops in proximity.
Companion planting is the concept of planting different crops in proximity, in an attempt to improve nutrient intake (eg. planting legumes with non-legumes), pest control (some plants can deter pests attracted to other plants), and pollination (plants attract pollinators which help other plants; or different varieties can be planted as non-producing pollinators for productive plants).
Companion planting has been practiced since ancient times, and by indigenous peoples. A well known example is the "Three Sisters" technique practiced by Native American peoples. This mixes squash, corn, and beans. The beans use the corn as a climbing trellis, and provide nitrogen fixing for the corn and squash. Nutritionally, these three crops also complement each other very well.
Pest control companion planting can work by deterring pests, or by introducing non-producing "decoy" plants.
Companion planting has traditionally been based a lot on folklore.