Gestalt is a psychology term which means "unified whole". It refers to theories of visual perception developed by German psychologists in the 1920s. These theories attempt to describe how people tend to organize visual elements into groups or unified wholes when certain principles are applied. These principles are:
Similarity occurs when objects look similar to one another. People often perceive them as a group or pattern.
The example above (containing 11 distinct objects) appears as as single unit because all of the shapes have similarity.
Unity occurs because the triangular shapes at the bottom of the eagle symbol look similar to the shapes that form the sunburst.
When similarity occurs, an object can be emphasised if it is dissimilar to the others. This is called anomally.
The figure on the far right becomes a focal point because it is dissimilar to the other shapes.
Continuation occurs when the eye is compelled to move through one object and continue to another object.
Continuation occurs in the example above, because the viewer's eye will naturally follow a line or curve. The smooth flowing crossbar of the "H" leads the eye directly to the maple leaf.
Closure occurs when an object is incomplete or a space is not completely enclosed. If enough of the shape is indicated, people percieve the whole by filling in the missing infomation.
Although the panda above is not complete, enough is present for the eye to complete the shape. When the viewer's perception completes a shape, closure occurs.
Proximity occurs when elements are placed close together. They tend to be perceived as a group.
The nine squares above are placed without proximity. They are perceived as separate shapes.
When the squares are given close proximity, unity occurs. While they continue to be separate shapes, they are now perceived as one group.
Figure and Ground
The eye differentiates an object form its surrounding area. a form, silhouette, or shape is naturrally perceived as figure (object), while the surrounding area is perceived as ground (background).
Balancing figure and ground can make the perceived image more clear. Using unusual figure/ground relationships can add interest and sublety to an image.
The word above is clearly perceived as figure with the surrounding white space ground.
In this image, the figure and ground relationships change as the eye perceives the the form of a shade or the silhouette of a face.
p/s: credit to link http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/gestaltprinc.htm coz give good example....