In Minecraft, there is a variety of language used to make talking about the game easier. Here's a quick glossary.

A chunk is the unit of the world map that Minecraft uses when it generates the world. Imagine it as a 16x16 grid of blocks spanning the entire height of the game world. That's 128 blocks tall, at least until Caves & Cliffs is finished releasing on Bedrock.

Chunks are relevant when setting things for graphics, simulation distance, slime spawning, and the location of buried treasure.

A mobile entity, enemy, or NPC. It's short for things like sheep, cows, spiders, skeletons, blazes, villagers, etc.