Very loosely, an invasion of a scale such that China most likely intended for it to establish direct control over at least half of the island of Taiwan, whether or not they actually accomplish this.
This is question #10 in the Astral Codex Ten 2023 Prediction Contest. The contest rules and full list of questions are available here. Market will resolve according to Scott Alexander’s judgment, as given through future posts on Astral Codex Ten.
China staged another round of “strike drills” around Taiwan this morning: https://www.reuters.com/world/asia-pacific/china-stages-drills-citing-us-taiwan-provocation-2022-12-25/