A spline is a mathematical function used to create smooth curves that pass through a set of points. They are commonly used in computer graphics, engineering, and data interpolation to model complex shapes and transitions. Splines can be defined in various forms, such as B-splines or Cubic splines, each offering different properties and levels of smoothness. In practical applications, splines help in designing objects like car bodies or animation paths. By adjusting the control points, designers can easily manipulate the curve's shape, making splines a powerful tool in both CAD software and 3D modeling.