A hum is a low continuous noise.
the hum of traffic.
低沉的车流声。
hums , humming , hummed
If something hums, it makes a low continuous noise.
The birds sang, the bees hummed.
鸟儿唱,蜂儿鸣。
When you hum, or hum a tune, you sing a tune with your lips closed.
She was humming a merry little tune.
她轻轻地哼着一首欢快的小曲儿。
If you say that a place hums, you mean that it is full of activity.
The place is really beginning to hum.
这个地方真的开始热闹繁忙起来了。