Interstellar
This is usually used to mean “outer space” in general, but it technically means “between stars” or “between solar systems.”
Most things whizzing through space are in an orbit of some kind. They’re either orbiting a planet (like a moon) or a star (like the planets around our sun). Something that is “interstellar” is not orbiting anything. Rather, it’s traveling across star/solar systems – flying through them and coming out the other side.
This is actually pretty rare (see below). I assume anything truly interstellar would need massive velocity and energy to avoid getting sucked into the orbit of whatever it flew past (and some interstellar objects probably cease being interstellar when they fly past something big enough to suck them in).
Why I Looked It Up
I found this article: US military confirms an interstellar meteor collided with Earth
An interstellar meteor is a space rock that originates from outside our solar system – a rare occurrence.
From Wikipedia:
Oumuamua is a known interstellar object detected passing through the Solar System. It is possibly the second interstellar object known; the first being a purported interstellar meteor that impacted Earth in 2014.
Postscript
Added on
I was thinking about the other day, and here are some other “inters,” based on other space scales:
Interplanetary, meaning from planet-to-planet. We’ve done this already, sending the Mars rover to that planet. It’s about eight months of travel time. We could actually get to Mercury or Venus much faster (about a month), but they’re far less habitable.
Interstellar, meaning from star system to star system. The nearest star system to us is Alpha Centarui, which is 4.3 light years way. This is 25 trillion land miles. This makes it about 180,000x further away than Mars, which means the nearest place we could travel “interstellar-aly,” would take somewhere over 120,000 years to get to.
Intergalactic, meaning from galaxy to galaxy. The nearest galaxy to The Milky Way (ours) is Andromeda, which is 2.5 million light years away. The time to travel there using current technology would be millions and millions of years.
"Inter-universal”… but there’s no such thing; the universe is the largest construct, and we know of nothing (physical) beyond its boundaries.
This is why all science fiction shows have “hyperspace” or “warp drive” or “worm holes” (or suspended animation on “generation ships”).
Beyond interplanetary travel, nothing else is realistic. Even to get the edge of our solar system takes about 35 years (Voyager 1 made it in 2012, having been launched in 1977), and then you’re in “deep space” (technically the Interstellar Medium) with nothing else for another 120,000-ish years (assuming you travel in the right direction and nothing kills you).