Weapon recharge rate. They only start at maintence level, so if you fire them consistently enough they run out of energy. You can use one of the F keys, like F9, or 10, or one of those to shunt power to your lasers, but it generally takes away from your engines and makes you slower.
Read a good faq or the game manual available on darksaber's site
(right side of the site has a block ad, says "DOWNLOAD THE PDF XWA MANUAL") you can't miss it.
You have to do some reading, 'cause energy management and transfer is the beating heart of the xwing series, you'll constantly be adjusting your rates to maximize speed shields or weapons or some combination there-of.
Moving energy from weapons to shields and vice versa is essential as well. And the game has no tutorial for such.
Learn your wingman commands (both hotkeys and through the CMD menus) and advanced targetting controls as well.