Here's why:
* Idiom: It's an expression with a meaning that is different from the literal meaning of the words. It means that words are easy to say but actions are more difficult.
* Proverb: It's a short, well-known saying that expresses a common truth or piece of advice. It warns against empty promises and emphasizes the importance of action over words.
So, while it fits both categories, "talk is cheap" is more commonly understood as a proverb due to its widespread use and direct advice.