An R-tree is a data structure used for indexing multi-dimensional information, such as geographical coordinates or spatial data. It organizes data into a hierarchy of bounding rectangles, allowing for efficient querying of spatial relationships, like finding all objects within a certain area. R-trees are particularly useful in applications like geographic information systems (GIS), computer graphics, and robotics. They help speed up operations such as searching for nearby points or determining overlaps between different spatial objects, making them essential for managing large datasets in a structured way.