Ever hear of NOTAMs

It is a compilation of notices that pilots read before going flying. You may see a NOTAM telling you not to fly near some parts of Delaware because Biden is there on vacation for example. An airman noted that among the NOTAMs he was reading waring of things like volcanoes and violent storms was a warning about 'weather modification'. It was somewhere near some islands in the Pacific. What is weather modification and why would there be a NOTAM warning of it?