While the leaders negotiated, the public held their breath.

held 是动词 hold 的过去式，hold 的意思是"握住、保持"。 their 是形容词性物主代词，指代"他们的"。 breath 的意思是"呼吸"，指一次吸入或呼出的空气。 held their breath 是一个固定短语，字面意思是"屏住呼吸"，比喻紧张地等待某事的结果。