A " nod" is the up and down movement of the head.

“nod（点头）”是仰头和低头的动作。

It's really going to be lots of up and down movements.

这真的会有很多上下的动作。

The up and down movements in the voice can show meaning or emotion.

声音中的上下语调变换可以表达意思或情绪。

Fluctuation is the up and down movement.

波动是上下运动。

So, the intonation refers to the up and down movement of your voice when you are saying something or reading something.

因此，语调是指当您说某事或阅读某事时声音的上下移动。