It usually means too much fuel or not enough spark.
If you think to black soot this is formed from tiny carbon particles.
The black deposit produced represents soot particles, heated to incandescence. It comes about when the combustion of air is insufficient.
Soot
yes, Egyptians did invent black ink.
A small stable flame of a candle has a lot less black smoke than a larger flickering flame. Air around the burning candle causes this to happen.
burning oil
running too rich check the air filter could also be defective injectors
You have worn valve seals and posibly bad valve guides.
Catalytic converters clog due to the carbon that the car produces. Usually, when the carbon has built up inside the cat., black smoke will come out of the tailpipe when you rev the engine. In extreme cases, black soot is visible on the ground next to the vehicle's tailpipe. Crystal Woll
Excess fuel causes black smoke.
Running rich, depending on year of vehicle it's possibly a o2 sensor, fuel system problem, carb if so equipped. Time for you to do some diagnostics
oil getting by the rings causes white smoke and oil dripping out of the tailpipe.
bad rings or really bad valve seals.
The city bus emitted a steady stream of black soot from its tailpipe.
water
You are burning oil.
soot