What kind of adverb is hardly?

"Hardly" is an adverb of frequency. It indicates how often something happens, in this case, "almost not at all" or "rarely".

Here are some examples:

* "I hardly ever eat sweets." (meaning I eat them very rarely)

* "He hardly spoke during the meeting." (meaning he spoke very little)

* "There was hardly any food left." (meaning there was very little food left)