There’s a big difference between ‘noise-isolation’ and ‘noise-cancellation’. The former simply minimizes the amount of external sound that gets into your ear based on the physical design of the earcups. It may also be referred to as ‘passive noise cancellation’. Basically, these headphones or earbuds block out noise by creating a snug fit and good seal between your ear and the outside environment so you can focus more on the desired sound at hand. Over-ear models that fit all the way around your ear have thickly padded cups designed to block out as much outside noise as possible.
On the contrary, active noise-cancellation makes use of a technological method for reducing unwanted sound by adding a second sound specifically designed to cancel the first, thereby eliminating external sound outside your headphones.