Coordinates are a system used to determine the position of a point in space. In a two-dimensional plane, coordinates are typically expressed as a pair of numbers, such as x, y, where x represents the horizontal position and y represents the vertical position. This system helps in mapping locations on graphs, maps, and in various fields like geography and engineering. In three-dimensional space, coordinates are represented as a triplet, such as x, y, z. Here, z indicates the depth or height of the point. This three-dimensional system is essential in fields like architecture, computer graphics, and physics, allowing for precise modeling and visualization of objects in space.