It allows specifying the Theme class to style all the Table control and Responsive Table cells of a row.
The property is available for the TableRow class in the Theme (and its descendants), and it's also for the Tables and Free Style Grid control.
The Cell Class property can be assigned to the TableCell class (or any descendant of it).
Cell Class property at the Theme
Cell Class Property of the cell of a Free Style Grid.
Objects Web Panels, Web Transactions
Row Class Property