An isometric view (or projection) of a 3D scene is a 2D picture of the scene in which parallel lines appear parallel. Like orthographic views, isometric views appear somewhat flat, due to the absence of normal perspective. The difference is that isometric views need not be drawn along one of the scene's main axes.
In mechanical drawing, isometric views are always drawn from a particular viewpoint that shows all three main axes at the same scale. This allows accurate measurements to be easily made. (The word isometric comes from iso, meaning same, and metric, meaning measurement.)
Blender, which can easily generate isometric views from any viewpoint, allows you to change the viewpoint (move the camera around in the scene). This enables you to see different sides of the object from different angles. Parallel lines remain parallel, but edges are drawn at different scales due to foreshortening.