Plus and Minus Barrels are one of the types of Barrels found in Donkey Kong Country 2: Diddy Kong's Quest, specifically the level "Haunted Hall". Their purpose was to keep the Kackle from hurting the Kongs.
A timer will start at the beginning of the level, and if the time runs out, the Kackle will get one of the Kongs. Collecting the Plus Barrels increase your time limit, and collecting the Minus Barrels will deplete it. Minus and Plus barrels serve no other purpose.