Overheating in Eve is the act of pushing your modules beyond the factory warranty and deliberately causing them to overheat and eventually burned out totally. They will crisp up and fail to function if you keep doing it.
Anyone that attempts to PvP in Eve should be familiar with the concept of Overheating (OH). It is the primary tool/skill that you can use to overcome your enemies and bring some small advantage to your own ship.
I want to underscore this point - I use OH, in one way or another, on every single fight. That is how important it is.
Evelopedia has a good starter guide on Heat and how it applies across your modules, I strongly suggest you read it and learn it. As does the Uniwiki.
(I'm sure there are others as well, use your own Google for goodness sake!) Learn it.
This post isn't actually about the science of OH, it is actually about the art of managing it in an actual fight. As usual in Eve, all the guides and science in the world are not going to help you much in actual combat. Actual combat in Eve is more Art than Science. If you don't know this already, it is about time you learned it.
But you have to know the science in order to perform the art. There are no shortcuts in Eve. But there are keyboard shortcuts. And using them is the ultimate step that makes someone a true PvPer in Eve. If you just finished reading that sentence and "poo-poo'ed" it, then you need to go back to your carebearing ways. Learning and using keyboard shortcuts is essential to PvP. And in no other place is this more obvious than in the activation and managing of OH in combat.
Each module has a F key relationship and I organize my mods on every ship in exactly the same way each and every time. Shooter, Point, Web, Thingie 1 and Thingie 2, Prop Mod, are the top rack. Damage Control, Rep/Boost, Xtra Thingie(s) are the second rack. Only the activation mods are shown, everything else is unimportant. (Thingies are mods like nuets, TDs, ECM, etc) The first and most important of these is reserved for locking target. Faster lock means applying damage faster than your enemy, so many fights are won simply because you started first.
Unlike the sample art above, I don't typically split the prop mod simply because I rarely heat an entire rack of mods. ( And remember, organizing your mods here is totally different than organizing them on your ship! That is an entirely different science, but equally important.)
You can heat mods in several different ways. You can heat an entire rack by clicking on those tiny little buttons to the right of the Big Circle, or you can click on the tiny little green bar at the top of each mod. Never do this. Shift+click to OH or stop OH'ing a mod. ("Never" defined as extremely rarely, obviously this is art so things vary on the situation at hand.)
Since this is Eve the ability to tell exactly when your mod is in danger of burning out on you can be difficult to distinguish in the heat of battle. And this is where things start to get into the realm of "bummer city" in my opinion.
The heat of battle is an instinctual reaction based blur in which you have very little time to think, plan and debate. You simply act. The UI is not very helpful in these situations and, in point of fact, can work against you. Modules flash in various shades of green and red, bars fill up, and the visual representation of activated, heated or not-heated can get a tad hard to follow. Not in a huge leisurely fleet battle, but in a one on one head bashing, ship on ship fight.
But, again, Art over Science. I would prefer a more clearly defined "edge" to each of these actions. Especially once combat is engaged and you are down in the trenches managing your mods, it can get rather complicated. Especially for certain, more active-minded, ships. Not only are you managing OH, but you are also turning things off and on to manage cap, the engagement, range, etc. A more clearly defined "edge" would be extremely handy at those moments.
Yesterday I had two perfect examples of both the positive and negative aspects of those challenges. Both involved toe-to-toe fights and both involved bad feedback from the modules resulting in different outcomes. In the first fight I was managing my prop mod in close combat, mindful of cap, the enemies position, and incoming damage. The feedback of OH damage to my mod was not accurately defined and it burned out on me when it wasn't supposed to. Or didn't 'look' like it was supposed to. I won the fight anyway, so no harm, no foul.
The second fight went the other way. While I pre-warmed the mods I wanted to pre-warm before the engagement, they actually were not pre-warmed at all. Despite 'looking' pre-warmed, when activated, they proved not to be. A more clearly defined "edge" would have given me this feedback before I committed to the engagement. Not after. My foe had the edge and won the fight.
I am a professional combatant in Eve. It is really all I do. What I am asking for is subtle and relatively meaningless in the greater context of Eve. I also don't believe it is all that difficult to make happen. Less glow and more go is what it essentially boils down to. The transition of the mod between two states can remain unchanged, just put it in the background. Think about how your cloak works as an example of what I mean. Either a mod is on OH or it isn't. Visually, just that one small change would make the world of difference.
When most solo or small gang combat takes place in about 30 intense seconds, it is the small things that really matter.
This post is not intended to serve as a guide to OH or Keyboard Shortcuts, there are many wonderful and exhaustive guides to these features available. I suggest you read and study them.