During his important presentation, he suddenly lost his voice.

lost 是动词 lose 的过去式，lose 的意思是"失去、丧失"。 voice 的意思是"声音"，指人说话或唱歌时发出的声音。 lose your voice 是一个固定搭配，字面意思是"失去你的声音"，实际指"突然说不出话"或"失声"的情况。