For satellites that revolve close to earth, it is much easier and fuel-economic to slow it down and let it fall back into the earth. If the satellite is small, it will burn and disintegrate completely in the atmosphere, just like hundreds of meteors do everyday. But if the satellite is large and there is the possibility that it might not burn up completely in the air, then retiring them requires a bit more planning.
The idea is to guide the satellite down into the ocean away from any significant landmass and human habitation where there can be no risk of injury from falling debris. The chosen place must also be far from shipping lanes. Such a spot in the ocean exist, and geographers call it the “oceanic pole of inaccessibility”.