Whats the difference? Yes, I had the same question when I was creating the custom page layout for my new articles. I didn’t know which one to pick. And yes, I googled.
In short, oslo doesn’t have the left pane which is more for the publishing sites; seattle provides the left pane, the standard SharePoint team sites we normally see are built from it.
Interesting fact: Oslo is a city in Norway, and Seattle in USA, flight duration is 11h50m 🙂