You used "meaningful" in your question. Not "rewarding" or "valued" but "meaningful."
What I find most meaningful is the productive interactions with colleagues and coworkers. Nothing successful at work comes in a vacuum. It takes input and action from a wide range of people with a wide range of backgrounds and wide range of lives outside of work. I'll have to remember this next time I interview for a job. It sounds like a great line, and I mean it.
"Productive interactions" isn't just some specific work thing, either. It's the friendly chat around the water cooler. Working well together is more than just everybody doing their work task.