Difficulty is an option in Minecraft which can be toggled via options menu. The difficulty setting determines how quickly a player's Hunger points deplete on their food bar, the frequency of Mobs spawning, mob strength, damage dealt by starvation, etc.
No mobs will spawn, and the food bar will not drain at all. The only food which can be eaten while the food bar is full is a Golden Apple or, if the difficulty was changed to peaceful when hungry, any food can be eaten until the bar is full again. The downside to playing on peaceful is the player can't get hostile mob drops and Experience cannot be obtained from said mobs. Playing on peaceful will also prevent a player from fighting The Wither, as Wither Skeleton skulls cannot be collected.
Few mobs will spawn, and the food bar will drain slower than usual. Mobs deal less damage than usual, very rarely hostile mobs will spawn with Armor. Cave Spiders lose their Poison ability. Creepers will cancel their explosion if the player moves only a short distance away. If the hunger bar is empty, it will leave the player with (10 health) Zombies will not turn Villagers.
Mobs will spawn normally, and Food Bar depletion is average. Mobs deal a normal amount of damage. The cave spider mob can poison players in this difficulty, and the Wither effect can be applied. If a player's hunger bar drops to 0, it will deplete all the way down to . If a villager is killed by a zombie, it has 50% chance of turning into a zombie villager.
A high number of mobs will spawn, and the Food Bar will drain quickly. Creeper explosions are highly fatal, one explosion and a player is dead, unless they were wearing armor. If the hunger bar drains completely, it will slowly kill a player. Creepers will not cancel their explosion attack unless the player moves far away. Zombies can break down wooden Doors and Spiders may spawn with one positive Status Effect (swiftness, strength, regeneration, invisibility, and these effects are permanent). Skeletons and Zombies have a higher chance of spawning with armor and Tools. These mobs will also have a higher chance of picking up anything. On this difficulty, if villagers are killed by zombies, they have a 100% chance of turning into a Zombie Villager.
Main article: Hardcore
A very high number of Mobs will spawn and the Food Bar will drain very quickly. This mode is similar to hard, but if a player dies, he/she can never re-spawn. If the game mode was set to "Hardcore" when the world was created, it cannot be changed to an easier difficulty.
Note: Hardcore is not actually a difficulty, but a Game mode. When you play Hardcore, your difficulty gets locked on "Hardcore", it cannot be accessed otherwise.