Extra Deep Fitted: The term "extra deep" in this context indicates that the fitted sheet is designed to accommodate mattresses with a greater depth or thickness than standard mattresses. A typical fitted sheet may have a pocket depth of around 25cm (10 inches) to fit standard mattresses, but an extra deep fitted sheet like the one you mentioned has a deeper pocket to fit mattresses that are up to 40cm (16 inches) thick.
40cm/16" Drop: The "drop" of a fitted sheet refers to the length of fabric that hangs down from the sides of the mattress, covering the mattress's thickness. In this case, the fitted sheet has a 40cm (16-inch) drop, which means it will extend 40cm down the sides of the mattress, ensuring a secure fit even on deep or thick mattresses.