In square foot gardening, a 4-inch spacing refers to leaving a gap of 4 inches between adjacent plants in all directions within a single square foot area. This technique is commonly used in intensive planting systems where space is utilized efficiently by maximizing the number of crops grown in a small area. By providing this distance between plants, they have enough space to develop healthy root systems and access light without crowding each other's growth. In this method, careful planning is required to ensure that each crop's specific needs are met within their designated area so they can grow optimally while avoiding competition with neighboring plants.