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The first six views on the toolbar are orthographic views - Top (World Plan), Left, Front, Bottom, Back, Right.
If your model was enclosed in a box, these views reflect how the model would appear by looking directly at each of the box faces. If you "unfold" the box, you can see the relationship between the views.
Front View: Looks at the XZ plane of the World Coordinate System, while facing +Y.
Top View: Looks at the XY plane while facing -Z (down).
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