sure is an English word with multiple meanings depending on context:
1. As an adjective: certain, confident ("I'm sure about this")
2. As an adverb: definitely, certainly ("Sure, I'll help you")
3. In informal speech: used to express agreement ("Sure thing!")
4. As a response: indicating confirmation ("Are you coming?" - "Sure!")
5. In phrases: "for sure" (definitely), "make sure" (ensure)