What is the difference between `document` and `document.body`?

What is actually the difference between document and document.body?

For example, I have the following code:

document.addEventListener('click',function(){ 
document.write('You click me!') 
})

<div>Click anywhere</div>

What will be the difference if I use document.body instead of document ?

And what is actually the difference between document and document.body?

I tried to search online, but couldn't find any useful information.

Thanks for any responds!