The word "hypersonic" and "hypersonic weapon", or "impossible to intercept hypersonic missiles", used in pop science publications and news reports. No one knows what this means, and just thinks that any ballistic missile is a hypersonic weapon that's impossible to stop, which is not the case. The US and the Soviet Union hit hypersonic speeds with ballistic missiles in the late 1940s based on V-2 missiles captured from Nazi Germany. The Bell X-15 was a manned hypersonic rocket aircraft in the 1960s. The US deployed maneuverable medium range ballistic missiles capable of hypersonic speeds in the Pershing-II in the 1980s. The Soviet Union had mass produced air launched ballistic missiles capable of hypersonic speeds, the Kh-15. None of these were considered hypersonic weapons. And none of their modern day contemporaries, like the Russian Kinzhal or maneuverable Iranian ballistic missiles, are technically hypersonic weapons. That doesn't mean that they're bad weapons systems (in some use cases they are superior to hypersonic weapons), just not in the hypersonic class.

Hypersonic weapons aren't just about speed, but a class of weapon, to do with achieving hypersonic speeds within the earth's atmosphere on a non ballistic trajectory for the majority of their flight. Such as the Russian Zircon hypersonic cruise missile, US Dark Eagle hypersonic glide vehicle, China's DF-17/DF-ZF hypersonic glide vehicle. It's about flying within the atmosphere at hypersonic speeds.