A normal is the direction a face points. Renderers use it to tell the front of a face from the back, and to work out how light falls on it.
Drag a model to turn it.
Face normalsOne arrow per face, pointing straight out of it.Vertex normalsEach vertex can have its own normal, averaged from the faces around it. This is what makes smooth shading possible.Front and backThis square only draws its front. Turned away, it disappears.A flipped faceOne face points inward (orange arrow), so it draws from inside only and leaves a hole. Fix it with Flip Normals or Recalculate Normals.Flat shadingEach face uses its own normal, so every face is lit as one flat color.Smooth shadingThe same mesh with vertex normals. Light blends across faces and the sphere looks round. No faces were added.Smooth with sharp edgesSmooth sides, sharp rims: the cap edges keep separate normals. Tools call this auto smooth or marking edges sharp.