Also known as POV. The filmic convention designed to show what a character is seeing.
At its most basic, the POV convention consists of two shots: point-glance and point-object. Point-glance is a shot of the character (or characters) who's POV we are showing. In this shot we see the character giving some indication that he or she is seeing something.
Point-object is a shot of what said character is seeing, whether it be animal, mineral or vegetable (or the dark depths of Hell, for that matter). Generally, the point-object is framed in such a way as to match the eye-line of the character, although this is not always the case.
There are many variations on the POV convention. In Carl Theodor Dreyer's film, Vampyr, there is a scene with a traditional point-glance/point-object set-up, except that the character from the point-glance walks into his own point-object!
A more common variation is the elimination of the point-glance altogether. This is very common in horror films. Instead we have one continuous (generally moving) shot, putting the audience in the position of the unseen point-glance. (SEE The Evil Dead Trilogy, An American Werewolf in London, Alien 3) This technique was taken to whole new heights in Kathryn Bigelow's cyberpunk thriller, Strange Days. A central element of the plot is a strange technology that enables people to attach a device to their heads and record everything that the say, think & feel. The disks from these devices are sold on the black market. Throughout the film, there are entire scenes that appear to be one shot, all from the POVs of people doing various things (robbing a Chinese restraunt, having sex, raping & killing, etc.).