Final answer:
The Gestalt principle that describes our brain's ability to fill in gaps and see a complete figure in an incomplete image is known as closure.
Step-by-step explanation:
According to the Gestalt principles, the ability for our brains to fill in gaps in a visual image and perceive a complete, often complex, figure is explained by an organizing principle called closure. This principle states that we organize our perceptions into complete objects rather than as a series of parts, allowing us to 'see' the whole where it may not be fully depicted. For example, when viewing an abstract painting composed of incomplete circles and lines, we can perceive full circles and complete figures.