A special effect which converts the whole image into black and white except for one specific colour range. One the the most common examples is a black and white image with a bright red subject – the girl in the red coat in the film ’Schindler’s List’, for example.
A means of correcting converging verticals in architectural shots and other perspective issues. You can get ‘perspective control’ lenses which use complex lens adjustments to fix the problem optically, or you can use software with perspective correction tools.
A ‘rule’ of composition that says that pictures look best if objects are placed one-third of the way in from the edge or top/bottom of the picture, rather than being placed directly in the centre. It can be helpful, though calling it a ‘rule’ gives it more importance than it deserves.