This technique might be called 'Double Fan Padding', since it used frequently for making padded notebooks. I consider 'binding' to be more appropriate. A well-done job will result in an exceptionally strong book in which the paper is more likely to fail than the glued edges. The less well worked jobs damage this reputation considerably.
This method requires thin strips of glue to be applied to the edges and on both sides of every sheet of paper to make a well glued hinge.
The fore-edge of the book is held scurely in a press, vice, or with clamps, and the hinge edge is rolled over towards the front, and then the back of the book. This exposes a slither of each page to the glue brush.
Successful fan binding requires a fairly runny glue and quick application. If the glue starts to set then the pages will not slide over each other as they are fanned. The glue needs to act as a lubricant for long enough to allow slippage of the pages whilst fanning and then relaxing again. If you are too slow the pages will stick together in the fanned position.
On straightening the pages they should be firmly pressed together and clamped into shape. It helps to apply gentle pressure ~ working from the fore edge to the spine so as to squeeze glue out (rather than stick too much of some pages together ~ leaving sufficient glue inside to do its job ~ removing as much glue as possible to increase flexibility ~ being careful not to allow glue to spill onto the head or foot.
It is useful to attach a strip of mull whilst the glue is still moist. Patting it down well so that it absorbs as much glue as necessary ~ finally there is often an opportunity to mop-up any excess glue which, if left, adds a tiny bit of extra and unecessary strength, and more stiffness than may be desired (especially if looking for a flexible-back binding).
Compare all this with "No fan" binding  and "Single Fan" binding .
This technique might be called "Double Fan Padding", since it used frequently for making padded notebooks. I consider 'binding' to be more appropriate. A well-done job will result in an exceptionally strong book in which the paper is more likely to fail than the glued edges.