Shot/Reverse Shot

A shot/reverse shot is a technique used in filming which involves two characters, beginning with one character looking at another character in an opposite position. The camera then moves the shot over to the opposite character showing the first character which establishes that the characters are facing each other.

This video is from the series

'FRIENDS', this video 

is a very good example of 
shot/reverse shot between
two characters.

KATIE

This is another example of Shot/Reverse Shot, showing both characters expressions, the technique is used to show both characters expressions and used because the characters are shown facing in opposite directions, the viewer assumes that they are looking at each other.