what does "clench" mean? Could you give me some examples?

Native speaker’s answer
Rebecca
To "clench" means to tighten or close into a tight ball, especially when feeling anxious or nervous. It's used to usually refer to the fingers or hand, but in some cases is used to refer to the clenching of one's butt cheeks. Ex: He clenched his hand tightly from anger. Ex: His fist was clenched tightly.