Don't understand the difference between new profile and new app

What's the difference between a new profile or a new app of a specific website ?
BTW both don't seem to work well under elementary luna.

A new profile is a complete new midori configuration (new settings, history, ....).
A app is just a midori instance in app mode -> you can't change all settings (extensions) and it's for one website only (external links will open the default browser).

Thanks for the explanation but i still don't get why an average user should need this ?

The new app sounds like a web application to me and a new profile a thing which i still
don't understand and it seems for advanced users.

You can use one profile for work, one for normal use and another one for your google+ account (for privacy reasons).

I use midori web apps and I still don't know what it means.

Maybe the real question is how the feature is conveyed. The term profile is well-known technical jaron but still a very abstract concept and indeed discussions often show how it's a little disconnected from the actual use cases.

So let's go by use case:
1. Joe uses his web browser at home. He uses GMail and other Google stuff, somehow it all works together.
2. Maria uses Midori at work. She needs to separate work from private stuff, using two Google accounts and also two Facebook accounts.
3. Kim is worried about Amazon's logging of their shopping habits and uses a session for shopping separate from everything else.