PostGIS is an open-source extension for the PostgreSQL database that adds support for geographic objects. It allows users to store, query, and manipulate spatial data, making it easier to work with maps and geographic information systems (GIS). With PostGIS, users can perform complex spatial queries, such as finding distances between points or determining whether a point lies within a specific area. This functionality is essential for applications in urban planning, environmental monitoring, and location-based services, enabling better decision-making based on geographic data.