A deep foundation is a type of building foundation that transfers the load of a structure deep into the ground, reaching stable soil or rock layers. This method is often used for tall buildings, bridges, and structures in areas with weak surface soils. Common types of deep foundations include piles and caissons, which are driven or drilled into the ground. Deep foundations are essential in preventing settlement and ensuring stability, especially in challenging environments like coastal areas or regions with high water tables. By anchoring the structure to deeper, more reliable soil, deep foundations help maintain the integrity and safety of the building over time.