Mobs

 A mob is a NPC that you can encounter during your adventures. These include monsters, villagers and animals. Some mobs like monsters can only spawn at night, and if in sunlight will burn (excluding spiders and creepers). Animals only spawn when there is enough light and grass for food. A villager can only spawn when there is a suitable house to live in nearby. When there are at least 15 villagers an iron golem will spawn to protect the village. There are even mobs that spawn at any level of light, such as a squid which will spawn anywhere as long as there is water. Lastly some mobs only spawn in a certain dimension. There are many types of mobs, some will help you, others kill you, and some are just to make it more exciting.