The rule of thirds is a concept in video and film production in which the frame is divided into into nine imaginary sections, as shown on the left.
This creates reference points which act as guides for framing the image.
Points (or lines) of interest should occur at 1/3 or 2/3 of the way up (or across) the frame, rather than in the centre.
In most "people shots", the main line of interest is the line going through the eyes.
In this shot, the eyes are approximately 1/3 of the way down the frame and approximately 2/3 across the frame.
|In this shot, the horizon sits at 1/3 from the bottom. The tree is 1/3 from the right|