Linear Perspective is a geometric method of representing on paper the way that objects appear to get smaller and closer together, the further away they are.
Isometric Drawing is a form of three-dimensional projection in which all of the principal planes are drawn parallel to corresponding established axes and at true dimensions; horizontals usually are drawn at 30° from the normal horizontal axes; verticals remain parallel to the normal vertical axis.
Oblique drawings are designed to show a three dimensional view of an object. The width of the object will still be drawn as a horizontal line, but the depth can be drawn back at any angle.
In simple terms, orthographic drawings are views (front, side, top, and so on) of an object. An orthographic view is only one side.