A normal vector is a vector that is perpendicular to a surface or a curve at a given point. In geometry, it helps define the orientation of the surface in three-dimensional space. For example, if you have a flat plane, the normal vector points straight out from that plane, indicating the direction that is "up" from the surface. Normal vectors are essential in various fields, including computer graphics, physics, and engineering. They are used in calculations involving lighting and shading in 3D models, as well as in determining forces acting on surfaces in mechanics. Understanding normal vectors is crucial for accurately representing and manipulating shapes in space.