Flare may be:
• A whitish haze
• Geometric shapes.
Flare is created when you aim your camera toward a bright light source, such as the sun.
The light enters the lens and bounces around inside.
This causes the haze and geometric shapes.
In the photograph below, you can see the haze on the left edge and geometric shapes to the right of the green twirler.
Here are two more examples.
Flare can be good for a photograph if it adds romanticism, impressionism, fantasy, and so forth.
Flare is often used when doing a portrait.
If flare doesn't add anything to your photograph, use a lens hood or use your hand to cast a shadow of the light source on your lens.
The following techniques will reduce flare, but less noticeably than the above methods.
1) Remove filters from the lens.
2) Use a fixed focal length lens instead of a zoom.
A zoom generally has more glass surfaces, which may cause more flare, than a fixed focal length lens.
5) Use a smaller lens opening.
6) Make sure your lens is clean.
Use an adjustable lens hood, also known as a matte box, for optimum reduction of flare.
You can adjust the bellows depending on the focal length of your lens.
Be sure to press the depth-of-field preview button on your camera to make sure the matte box is not appearing in the viewfinder.