An octree is a tree data structure used to partition three-dimensional space. It divides the space into eight smaller regions, or "octants," allowing for efficient organization and retrieval of spatial data. This structure is particularly useful in computer graphics, 3D modeling, and spatial indexing. In an octree, each node represents a cubic volume, and its children represent the subdivisions of that volume. As objects are added or removed, the octree can dynamically adjust, making it effective for applications like collision detection, 3D rendering, and geographic information systems.