On what basis are the duplicate records identified during import?

On what basis are the duplicate records identified during import?

While importing records, there are options to overwrite, skip and clone the duplicate records. All the duplicate records are identified based on some fields for each type of record. Following are the fields for each type of record:

Leads - Email
Contact - Email
Account - Account Name
Potentials - Potential Name
Cases - Subject
Solutions - Title
Campaigns - Campaign Name
Vendors - Vendor Name
Products - Product Name