Symbol | Graphics Layer Overlay
Graphics are points, lines, or polygons that are drawn on top of your map in a layer that is independent of any other data layer associated with a map service. Most people associate a graphic object with the symbol that is displayed on a map to represent the graphic. However, each graphic in ArcGIS Server can be composed of up to four objects, including the geometry of the graphic, the symbology associated with the graphic, attributes that describe the graphic, and an info template that defines the format of the info window that appears when a graphic is clicked on.
Dynamic layer added to the map
Graphics are often used to represent information that is generated as the result of actions performed within a working application. Frequently, these graphics are returned as the result of a task that has been performed, such as an attribute or spatial query. This can include points, lines, polygon, and text. These are temporary objects, only displayed during the current browser session. Each graphic can be composed of geometry, symbology, attributes, and an info template, and is added to the map through the use of a graphics layer, which is always the topmost layer in an application. This ensures that the contents of the layer will always be visible.