A seller is an entity that can have one or no parent (such as a sales organisation).
It has a legal existence in one country, have a VAT number, a registration number, a currency and address.
Those mandatory elements are required for generating the invoices.
Invoice sequence list
A seller can have its own invoice sequence on one or another invoice type.
If no invoice list is defined, then this is the default seller one that will be used.
Here is an example of a seller that will prefix his invoices with BESTSELLER for the Invoice, credit note (ADJ) and quotes:
Customer sequence list
A seller can have its own sequence to be used on a script or any integration.
Here you can define its code, prefix and sequence size: