Floor joists are horizontal structural members used to support floors and ceilings in buildings. They are typically made from wood, steel, or engineered materials and are spaced evenly apart to distribute weight. Joists help create a stable framework that allows for the installation of flooring materials like plywood or laminate. These components are crucial for maintaining the integrity of a structure, as they bear the load of furniture, people, and other items. Proper installation and spacing of floor joists are essential to prevent sagging and ensure a level surface, contributing to the overall safety and durability of the building.