Pocket diapers consist of waterproof outer layer (lined with PUL or TPU just like the covers) but have cloth linings sewen together with the outer layer.  It has an opening where you can place the inserts for absorbency, thus calling it "pocket."  With this, you can use the inserts that usually come with the diaper or customize it with a prefold or hemp insert, making it adjustable to your baby's needs.