Special effects (SPFX) are used in the film, televsion, and entertainment industry to create effects that cannot be achieved by normal means, such as depicting travel to other star systems. They are also used when creating the effect by normal means is prohibitibly expensive, such as an enormous explosion. They are also used to enhance previously filmed elements, by adding, removing or enhancing objects within the scene.
Many different visual special effects techniques exist, ranging from traditional theatre effects, through classic film techniques invented in the early 20th century, to modern computer graphics techniques (CGI). Often several different techniques are used together in a single scene or shot to achieve the desired effect.
Special effects are often "invisible." That is to say that the audience is unaware that what they are seeing is a special effect. This is often the case in historical movies, where the architecture and other surroundings of previous eras is created using special effects.
Visual special effects techniques (in rough order of invention):