Balls is a common English slang term with multiple meanings depending on context.
1. Literally refers to testicles (睾丸), but often used metaphorically
2. Can mean courage or bravery (勇气), as in "He's got balls to do that"
3. Sometimes used as an exclamation to express disbelief (表示怀疑), like "Balls! That's not true!"
4. In sports, refers to the actual balls used in games (球类运动中的球)
5. Can be used as a vulgar term (粗俗用语), so be careful with usage