your body uses other calories mate.
even when asleep etc.
You're constantly burning energy just to stay alive. A few hours between session is not advised; you will not be building muscle. With weight training, your workout needs to be intense enough that you shouldn't be working out the group of muscles you've used again for the rest of the day, or the next, yet alone a few hours.
If you want to lose weight, getting some more muscle will help you achieve that, and muscle mass increases while they are recovering from training, not while you are working them out, so too much frequency is counter-productive. Also, if you feel you're able to do another workoult on those muscles later in the day, you're not working hard enough during your session and will not see optimal results.
Google 'Basal Metabolic Rate'.
As others have said, basal metabolic rate.
(Essentially, your body needs energy just to stay alive for basic metabolic processes. Like glucose gets broken down and ATP is formed from the energy released in the process, and this ATP is needed to keep things like the sodium-potassium pumps in cells running. And quite a lot of other cellular processes will also need energy!)
Lol @ exercise being nothing to do with BIOLOGY
Also you would have nothing to lubricate your joints.
OP - I wouldn't take the advice being proffered regarding weight training as a means to cutting fat.
While it is true that more muscle mass with cause you to burn more calories at rest, it's actually a lot more complicated than that, and adjusting the amount of anaerobic muscle in your body to any significant degree will affect how you metabolize all the food you eat. In my personal experience and what I have observed, you're better off sticking to cardio and circuit training if you want to tone up and lose bodyfat. Resistance training is obviously required if you want to build big muscle, but don't believe the rubbish some people will try to tell you that it will promote fat loss. You'll have to eat a lot more to avoid muscle damage/tearing and atrohphy, your appetite will increase as much as two or three fold if you really hit the weights, and you'll find it a lot harder to eat under your maintenance calories (and therefore burn fat reserves)