A product that your organization sells.
Pricebook2
A price book that contains the list of products (Product2 records) that your organization sells.
1. Each organization has one standard price book that defines the standard or generic list price for each product or service that it sells.
2. An organization can have multiple custom price books that can be used for specialized purposes, such as a discount price book, price books for different channels or markets, price books for select accounts or opportunities, and so on.
3. For some organizations, the standard price book might be the only price needed, but if you need to set up further price books, you can reference the standard price book when setting up list prices in custom price books.
PricebookEntry
A product entry (an association between a Pricebook2 and Product2) in a price book.
It represents a price for a given currency.
Cheers!!!