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.