system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between an ocean and a sea?

You always hear about "sailing the seven seas", so are oceans also seas, but seas aren't necessarily oceans? 

Edit: The reason I asked this is because Google says a Sea is usually a body of water that touches a landmass, but we don't call it The Pacific Sea when you go to the beach in California.
gpt
Seas are geographic locations of the oceans where land and ocean meet. There are more than 7 seas. Our oceans have general boundaries, but ultimately it's difficult to really tell where one ends and another begins. Our Earth has 1 ocean, we just geographically call areas of this 1 ocean: Atlantic, Pacific, Indian, Arctic, and Antarctic.