A vacuum is, by definition, a region of space devoid of matter. While a perfect vacuum is a physical impossibility, very good approximations exist. Interplanetary space is good, especially far from the sun. Interstellar space is better, and intergalactic space is even better than that.
Along come humans, then, and they invent these things:
. . . and call them “vacuum cleaners.”
Now, this makes absolutely no sense. There isn’t anything cleaner than a vacuum — and the closer to an ideal vacuum a real vacuum comes, the cleaner it gets. Since vacuums are the cleanest regions of space around already, why would anyone pay good money for a machine that supposedly cleans them? They’re already clean!
Even cleaning in general is a puzzle, without vacuums being involved at all. To attempt to clean something — anything — is, by definition, an attempt to fight the Second Law of Thermodynamics. Isn’t it obvious that any such effort is, in the long run, doomed from the outset?
[Image note: I didn’t create the images for this post, but found them using Google. I assume they are in the public domain.]