A horizontal datum is a reference framework used in mapping and surveying to define the position of points on the Earth's surface. It provides a baseline for measuring geographic coordinates, such as latitude and longitude, ensuring consistency in location data across different maps and systems. Common examples of horizontal datums include the North American Datum of 1983 (NAD83) and the World Geodetic System 1984 (WGS84). These datums are essential for various applications, including navigation, land surveying, and geographic information systems (GIS), as they help accurately represent the Earth's shape and size.