bash - What does {} means?

I want to delete files, which have size = 0. So I tried:

find ./ -size 0 |xargs rm

But it has a problem with files, which names begin with space. I found this:

find ./ -size 0 -exec rm -i {} ;

It works. I think my way with xargs is too sophisticated for this.

What does {} ; means? Could you explain me? My English is not very good, so please write simply.