What is the difference between a primary and secondary cell?

Cell as in battery cell. I understand that secondary cells can be recharged and used again, and that primary cells cannot, but I want to know why. What properties do secondary cells have that primary cells don't, that allows them to be recharged?What is the difference between a primary and secondary cell?
Primary cell: It is an electrochemical cell which acts as a source of electrical energy without being previously charged up by an electric current from an external source.



Secondary cell: The cell in which electrical energy from an external source is first converted to chemical energy and

then made to operate in opposite direction by removing the external source.

In this cell, the reaction can be reversed practically. It can be recharged after its discharging.



More clear cut explanation from the electrochemistry chapter from the following resource.