Star Barrels are barrels that you can can find in every level of the Donkey Kong Country series, except for bosses. When touched, it explodes, and leaves behind star dust-like powder. When you see it explode, you know that if you die, you will start at this point instead of having to start the level over. It is the "checkpoint" of the Donkey Kong Country games.
It usually floats in mid-air, so Donkey or Diddy need to jump to get to it. It is most often placed in a spot that makes it easy to hit it, though, so it's usually not a problem. It is located near the middle of the level, sometimes even closer to the end, making this barrel very useful since no one wants to start at the beginning every time they die.
In Donkey Kong Country Returns, Star Barrels are replaced by pigs that hold flags when passed.