It's when a spook is hung over and late for work because they drink to forget the times in Afghanistan where they had to give little boys to pedo warlords. The boss spook is pissed and demands an answer for why they were late.

"Sorry boss, got uhhhh hit by a microwave beam weapon"

Basically US spooks in Cuba/China/Russia feel weird, claim they have heard a weird noise for 30-ish seconds and then a while after they get examined and have some kind of brain damage.

The claim is that this is microwave weapons that are being used that somehow can damage someones brain that fast, from far away, and not target anyone in the vicinity, theres no evidence for this aside from "Microwaves could technically do this".

Havana syndrome is when a US spook feels unwell, can't/won't explain why and therefore blames secret Russo-Chinese Cuban sci-fi death ray weapons.

It's when you hear a strange new cricket for several months and think its tinnitus.