The player base has simplified many of the animals or enemies in the game to an umbrella term of “Mobs”. In Minecraft, you will encounter many types of living animals that typically pay you no mind. However, once you attack them they may retaliate. This forms the basis for neutral mobs in Minecraft.
Examples of neutral mobs include llamas, bees, dolphins, zombie pigmen, and many more. These mobs will typically mind their own business and will only intrude on the player when the player acts out aggressively towards them. Even if the player hits them by accident, a group of neutral mobs will attack a player that attacked them.
There are other conditions for certain mobs such as breaking a beehive or attacking villagers (bees and iron golems respectively), but for the most part, neutral mobs will leave you alone as long as you leave them alone.
Below you can find a detailed list of all the current neutral mobs currently in Minecraft.