A floor joist is a horizontal structural component used in building construction to support the floor above. Typically made from wood, steel, or engineered materials, floor joists are spaced evenly to distribute weight and provide stability. They are essential for creating a level surface and preventing sagging or bouncing in the floor. In residential buildings, floor joists are often part of a larger framework that includes beams and columns. They connect to the foundation and support the subfloor, which is then covered by flooring materials like carpet or hardwood. Proper installation and spacing of floor joists are crucial for the overall integrity of the structure.