Antipodes are specific points on Earth that are directly opposite each other. Hong Kong and La Quiaca, Argentina, are examples of antipodes.
If you drew a line from one geographical location straight through the center of the planet to another location, those two places are antipodes. If someone in the northern hemisphere refers to the Antipodes, with a capital A, they mean Australia and New Zealand (although inhabitants of the southern hemisphere do not refer to those places in this way). You can also use this word figuratively, to describe opposites: "My brother and I are total antipodes — he's sporty, and I'm a bookworm."