Oblique
This image represents an oblique sketch which shows the width and height of the shape, the shape is not in 3D.
Iosmetric
This next image shows the isometric sketch which shows depth, height, and width of an object, these objects have points which are 120 degrees
1Point Perspective
The lines that go to that point means the object is one point perspective drawing. the point that most of the lines on the object flow to is called the vanishing point
2 Point Perspective
Two point persective is the same as One point, but the only dioffernece is that the object has two vanishing points and as you can see the objects lines flow to two different directions on the object.
Multi-view
This kind of sketch allows you to view most or all sides of the object in 2D. Those dotted lines represent hidden lines which tells the observer there are areas there of empty space on the object. as you can see the way the multi- view sketch is used the size in length of the object is displayed for every view