Hardly is an adverb that means "almost not" or "only just". It's often used to indicate that something is barely true or barely the case.
Common usages of hardly:
1. Hardly + any/ever: "There's hardly any food left." (几乎没剩下什么食物)
2. Hardly + when: "I had hardly arrived when it started to rain." (我刚到就开始下雨了)
3. Hardly + can/could: "I can hardly believe it!" (我简直不敢相信!)
4. Hardly + ever: "He hardly ever calls me." (他几乎从不给我打电话)