Orcas are called "killer whales" because a long time ago, people saw them hunting and eating other animals, including whales. But the name "killer whale" can be a bit misleading because orcas are actually a type of dolphin, not a whale.

When people first saw these big, powerful animals hunting together and being really good at catching their food, they thought they were like skilled hunters. So, they called them "killer whales" to show that they were really good at catching their prey, not because they go around killing things all the time.

Imagine if you had a nickname that described something you're really good at, like "Super Soccer Kid" if you're great at playing soccer. It's a bit like that for orcas, but their nickname became famous and stuck around.

So, orcas are called "killer whales" because of their hunting skills, but they're actually a special kind of dolphin that's really amazing at catching food in the ocean!