A gestalt is a structure or configuration of physical, biological, or psychological phenomena so integrated as to constitute a functional unit with properties not derivable from its parts in summation.
Gestalt psychology in based on the unity of psychic life, the existence and primacy of psychological wholes which are not just a summation of elementary units. Basically, the parts of a shape only have meaning by the fact that they belong to a whole, that is, a shape cannot be split up into its elements without losing the meaning which it possessed as a whole. Thus human behaviour can be thought of as a gestalt, a mental whole which transcends the mere combination of its elements.