Concerning the Web application architecture what's the difference between domain classes and business classes?

I want to architect my asp.net web form application like this :

1-DB
2-Data Access Layer(Using ORM[EF])
3-Repository/Unit Of Work (Pattern)
4-Business Layer
5-Service Layer
6-UI

Right now my primitive solution looks like this :

Just two class libraries :

• DAL (Data Access Layer) where my EF resides in.
• Domain Classes (auto generated) with their equivalent partial classes.

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My questions concerning this design :

1. Should I put my business logic in a new layer or just in the domain classes layer where each business belong to the related domain class Or put my business logic in the code behind of my web pages ?
2. Could some one clarify what's the difference among those terminologies in the design perspective (POCO,Domain Class,BusinessClass)?