Learning what fire actually is, like what the flames are literally made of, blew my freaking mind years ago.
Fire is literally just gas (and fine solid particulates suspended therein) that contains so much thermal energy that its black body radiosity has reached into the visual spectrum.
There are some types of flames that are NOT bright enough to be visible under ambient lighting conditions and can only be seen in environments that are very dark!
Pure ethanol, for instance, combusts dark enough that you can't see the flames in daylight conditions, or even under strong artificial lighting.
I had an RC car as a kid with a small combustion engine that used methanol. When I and my friend realised that methanol burns without a flame we got so excited. It brought a new dimension to our army men shenanigans. That and discovering home made napalm.
I don't understand why some people do it, it's just such an insanely shitty thing to do that doesn't seem like it'd have any benefit whatsoever (not saying it was the OP, these tend to float around the internet.)
Probably doesn't help that every consecutive year of physics education is like "anyway everything we taught you last year is a simplification that's technically wrong. Here's how it really works now that you know enough math to understand the next level"
Technology Connections is the shit! The episode on hurricane lanterns is great and has a stupid joke in there that comes so far out of left field it killed me: https://youtu.be/tURHTuKHBZs
Fire is a sustained chemical reaction where carbon-based molecules are broken up and combine with oxygen, releasing carbon dioxide, sometimes methane, and heat (and thus light), which primes the remaining carbon-based molecules for continued chemical reactions with oxygen.
Firstly, the definition from Wikipedia: Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
For all you bad cooks out there, the reason you can't burn water when you're cooking is because water is already fully oxidized. Water is also often one of those reaction products the definition talks about.
I other words, you can't burn water because it's already burnt.