What does "reserve take off" mean in engine parameter documentation?
I've seen this mentioned in story (unfortunately in Czech) about flying in Bhutan on ATR-42 (a smaller version of the same aircraft). Basically in most situation it is recommended to use less then maximum rated power to reduce wear of the engine and that setting is marked as “take off” and the maximum rated power is only used in high density altitude (hot and high) conditions or very short runways and is labelled “reserve take off”.

Most other aircraft don't have setting labelled like this, but taking off at less than maximum rated power is common. It is called “derated” or “flex” take-off.