It’s a fair, good question. Not super easy to answer.

I use it in the Buddhist sense, though I don’t call myself one. Even there you’ll get different answers. But its generally a kind of presence of mind. It’s not occupied on things in another place or time, it’s experiencing its environment clearly. Uncluttered. A kind of vigilant meditative state, almost. It’s aware of what’s happening, acknowledges it, and carries on.

I hope that helps.

Paying focused attention to your senses, surroundings, and thoughts. Unlike meditation that tries to change how you feel, mindfulness is letting excess thoughts go so you can focus on what happening right now.

Helps when things feel overwhelming and is the only meditation my ADHD self can do.

I think you’re looking at correlation more than causation. That’s what the enlarged gas tank metaphor in another comment here is trying to hint at.