Hi Aisha,,

A lot number (also called serial number in Odoo) can be considered as a serial number for a single product, or a batch containing quantities of a certain product. Lots are typically used to identify a serial number (for a computer, printer, ...), or as production lots to indicate for instance quality grades or delivery lots. You can make it mandatory to enter a lot number according to the incoming/outgoing/full traceability options ticked in the Product Variant form. 

You can get more information from : https://www.odoo.com/forum/how-to/warehouse-management-6/whats-the-difference-between-quants-lots-and-products-55243