From BlenderWiki
Display panel
This panel lets you configure some visualization parameters of the viewport.
When Only Render is ticked, only renderable objects are shown; things like lamps, empties, cameras, speakers, the grid (and its axes), relationship lines, object origins, selected objects outlines, or the 3D cursor are not shown at all. However, 3D manipulators are still visible (except for rendered view mode, in which those are never shown).
Outline Selected outlines the selected objects in an orange colour.
All Objects Origins shows the origin of all objects, and not just that of the selected ones.
Relationship Lines shows object relations using dotted lines (hierarchy, constraints, etc.).
In wireframe shading mode, mesh objects are drawn using a simplification of their topology. However, ticking All Edges, mesh objects will be drawn using all their edges.
Grid Floor is related to the finite grid that is shown in views other than the predefined orthographic ones. This "floor grid" lays on the global XY plane. This control lets you show or hide that grid.
X, Y and Z are used to activate/deactivate the visibility of coloured lines indicating the position of global axes in the "floor grid". Their length depend on the defined size of that grid.
Lines defines the number of lines that will make the "floor grid" up. If N is the number defined, there will be a total amount of N/2 lines at each side of X and Y axes. For odd values of N, the amount of lines will be rounded down.
Scale defines the distance between grid lines, either in the "floor grid" and the infinite grid.
Subdivisions defines the amount of lines into which the infinite grid should be subdivided. Level of subdivision depends on zoom, in predefined orthographic views.
Toggle Quad View toggles quad view on or off.
