Is space a vacuum?

Is space a vacuum, yes, outer space is very close to perfect vacuum, though not absolute perfect vacuum, because it has extremely low pressure and very few particles compared to Earth's atmosphere. At sea level, atmospheric pressure is about 101 kilopascals with billions of molecules per cubic centimeter, while in low Earth orbit where International Space Station orbits, pressure is around 1e-7 pascals with few particles, and in interstellar space about one atom per cubic centimeter, and in intergalactic voids even fewer. So space is considered high vacuum to ultra-high vacuum by engineering standards, essentially empty. However, space is not completely empty, it contains some hydrogen atoms, cosmic dust, radiation, and magnetic fields. Perfect vacuum with zero particles does not exist naturally. Because space is vacuum, there is no air to breathe, no sound transmission, no convection, and exposed liquids boil quickly. This vacuum property is used for testing spacecraft in vacuum chambers on Earth. So yes, space is a natural vacuum, close to best vacuum we can create, which is why astronauts need pressurized spacesuits and spacecraft.