An animal makes humming sounds when it's happy or excited.
When birds sing their sweet melodies, that sound is often called humming too. We might say "the hummingbird sang its beautiful song" to describe the bird's musical trill. Some insects, like bees and wasps, also hum as they fly around, usually because they're buzzing with energy.
How common is "humming"?
Word humming is considered rare in modern English. It appears most frequently in fiction texts and less often in other writings.
Definitions
verb
To make a sound from the vocal chords without pronouncing any real words, with one's lips closed.
Example: We are humming happily along with the music.
To express by humming.
Example: The team ominously hummed “We shall overcome” as they came back onto the field after the break.
To drone like certain insects naturally do in motion, or sounding similarly
To buzz, be busily active like a beehive
Example: The streets were humming with activity.
To produce low sounds which blend continuously
To reek, smell bad.
Example: This room really hums — have you ever tried spring cleaning, mate?
To flatter by approving; to cajole; to deceive or impose upon; to humbug.