These are not limited to Minecraft-looking assets, with many mods made today being a crossover from other games or themes. Specific to Minecraft, mods can add more actions, abilities, items, animals, hostile mobs, and environments to your character or world, apart from simple cosmetic changes. These mods can affect how the game looks, similar to how Minecraft shaders alter the gameplay slightly or drastically.
Mods or modifications are extra and replacement content usually created by third-party developers.