When drawing orthographic drawings, the observer present a 3D image in two dimensions.
When producing an orthographic drawing you will generally produce three views. A plan view,end elevation and a front elevation. The plan view is the view of objects when we look directing down on the top of the objects End elevation is either or sometimes both the remaining side views. Last but not least, front elevation is the view when we look straight on the front of the objects.
Drawing taken from: www.hollyzell.com/ art121a.htm