Minikits are black LEGO canisters with the bat emblem on them, that serve as a collectible in the LEGO Batman games.
Minikits can be found in mission levels, where there are usually 10 per mission to be collected. Usually players will have to go out of their way to get them, wether it be scour a hidden area, destroy multiple of the same objects, or solve a puzzle. Many minikits require the use of Free Play mode to be accessed by a character with the right abilities.
The minikit also happens to be the main icon for the LEGO Batman Wiki.