What is the hole in the vacuum cleaner?

I've always been puzzled by this as literally all of the vacuum cleaners has a hole around the top part of hose area, but I can't seem to figure out the uses of it. It comes with a plastic part in which you can open or shut the hole when vacuuming. If somebody knows the uses of it, please let me know Thanks! show more I've always been puzzled by this as literally all of the vacuum cleaners has a hole around the top part of hose area, but I can't seem to figure out the uses of it. It comes with a plastic part in which you can open or shut the hole when vacuuming.
If somebody knows the uses of it, please let me know
Thanks!
4 answers 4