What is difference between domain class and entity class in entity framework ?

Typically, the domain object defines the business object and it's properties and methods. It's used to manipulate and move the data within the processing system. The Entity object exists to take those domain properties and map them to a persistent storage object, such as a database table.

Using a mapping tool such as AutoMapper will do the mapping of the domain object to the Entity object, or you can code that separately if desired.

In the example below the persistent storage is a database table called BookInformation, which has columns BookId, Book_Title, and Book_ISBN.
That entity object is defined in the class BookEntity.

The domain object class Book is defined with 3 properties, BookID which is a database generated GUID, the BookName and the ISBN.

// Domain object
public class Book
(
	[Key]
	[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
	public Guid BookId {get;set;}
	public string BookName {get;set;}
	public string ISBN {get;set;}
)


// Entity Object
[Table("BookInformation")]
public class BookEntity
(
	[Key]
	[Column("BookId")]
	[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
	public Guid BookId {get;set;}
	
	[Column("Book_Title")]
	public string BookName {get;set;}
	
	[Column("Book_ISBN")]
	public string ISBN {get;set;}

)