What does it mean when you go out on a date with someone?

What does it mean when you go out on a date with someone?
It's hard for me to explain the situation I'm in (there are a lot of side stories which I can't explain here... I'll keep it concise). I like my best friend. She doesn't feel the same about me. We went on a date once. But since then I've tried to keep our relation STRICTLY FRIENDLY.
The reason being that she doesn't feel the same way for me... And being the way we are is creating a lot of trouble for her as well as for me.

She asked me if I would ever wanna go out with her again. Obviously I do... So I asked her: hangout as friends or a date? And she says date. And I decline the offer.

She said that I've made up my mind that friends can't go out on dates. The thing that bothers me is that, when it's not gonna happen (she made it very clear) then why would I ever go out on a date with her.
To me dating is something what couples would do or at least you go on a date to get to know the person more before committing to them. But in my case, we know each other way too well and have made it quite clear that we will never be a couple. So should I go on "dates" with my best friend?
What does it mean when you go out on a date with someone?
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