But seriously, a bolted fault is a term used by folks, and most often associated with discussing or performing fault current calculations. The condition applies to SLG, LL, LLG, and 3phase faults where you assume the impedance between the lines and ground, or between the faulted lines is zero. However, this is an assumption becasue unless you purposely create this condition, all faults have some impedance.
There are multiple reasons for assuming a zero fault impedance. The first is that since every fault condition is unique, it would be physically impossible to know this value in determining fault current levels so it would be arbitray anyway. Second, is that in the calculations this impedance simply reduces the fault current from the maximum possible and therefore if the wrong value was used (to high), it could lead to improperly rated equipment. The real world impedance is typically so small that the reduction would not affect the rating of the equipment, or normally change the level in which you would select a relay to trip. To include it, would mean an arbitrary number is used anyway, and therefore provides no real value in attempting to use it.
On the flip side, every fault has some impedance involved in the faulted connection. If a distribution line goes down over a tree, the impedance is very high, and the relay may not trip, unless other parameters are looked at, and this is why line relays react on other parameters as well.
The difference in fault current and arc flash current is that arc flash calculations include a reduction for the impedance in the fault.
