In the Battlefield games, certain weapons—especially machine guns—can only be fired in bursts. Each bullet shot adds a specific amount to a heat gauge. The gauge drains at a steady rate. Should the gauge reach maximum (overheat), firing ceases, and the gauge may drain at a slower rate until it is empty again.
In Battlefield 2, light machineguns each have a different "heatAddWhenFire" value which determines the point at which the weapon overheats. Every time the weapon is fired, the value of heatAddWhenFire is added directly to the heat value (starting from zero). Essentially, when the total heat value meets or exceeds one, the weapon goes into an overheat state and then cannot be used for the weapon's overheatPenalty time. The heat value is decreased (when not firing) by 0.2 per second, back to a minimum of zero.
Heavy machineguns share a similar pattern -- all heavy machineguns (except for the M134) have their heat value increase by 0.02, cool down by 0.4 per second, and have an overheat penalty of 3 seconds. The M134 differs only in that its heat value increases by 0.01.
The mounted light machineguns have heat increase by 0.01 per bullet (except for the RPK, which increases by 0.013), and share the same cooldown and overheat penalty as the heavy machineguns.
Although each weapon could potentially have separate cooldown and overheat penalties, all light machineguns share the same values for these fields. Ergo, all light machineguns have an overheat penalty of 1.2 seconds, and cool down at a rate of 0.2 per second.
The term "cooldown" may also be applied to other time constraints, such as reloading, weapon switch, or swapping.
Certain abilities that can be reused have a cooldown timer: