Mobs in Minecraft are living, moving creatures in the game. The word "mob" is short for mobile. Mobs are affected by physics and gravity the same way as the player. They are affected by the environment the same way as the player; they are harmed by fire, lava, drowning, weapons, etc. 

Some mobs may me more resistant or immune to hazards, such as Nether mobs who are immune to fire and lava. Mobs can ride minecarts and other mobs. They can also climb ladders. When mobs are killed, they usually drop useful things for the player to pick up. They also have a pathfinding system that lets them navigate complex mazes. 

Each type of mob has their own type of artificial intelligence (AI), which determines their behaviors and mechanics. Mobs usually randomly wander around and avoid falling off cliffs and high blocks.