Basically Perspective Drawing is too like reenact a scene from a persons point of view, which is the vanishing point. But without the point, the drawing cannot be understood.
Isometric Drawing is a 3d picture in which the drawing is not viewed from a right angle, thus when drawing it, the lines which are drawn from the centre of the drawing must be 30 degrees or so.
Oblique drawings are designed to show a person the 3d image of an object but it is not a 3d image. it is instead a 2d image which shows you clearly a side of the image but the rest of the image is distorted, hence making it look like a 3d picture.
Orthographic drawings are drawings that shows the shape and size of an object through a series of related 2d views.
Ho Jun Hui