What is Diffraction?
Diffraction refers to the effects of a wave (i.e. Light) after it has come into contact with some kind of obstacle. For example, when a light is shone towards a metal plate, that it can't pass through, but which has a small slit in the middle, the light will pass through the slit and on the other side will spread out in a cone shape. You can see this effect if you stand in a darkened room adjoined to a room with a light on - you will see the light diffract through the doorway opening and spread out into the room you are in. Another example, using water instead, is the way waves spread around objects they encounter in the ocean - a boat will cause oncoming waves to diffract as they pass around it.