TableDepth is an option for TableForm and MatrixForm which specifies the maximum number of levels to be printed in tabular or matrix format.
TableForm[list, TableDepth -> n] prints elements in list below level n as ordinary lists, rather than arranging them in tabular form.
With the default setting TableDepth -> Infinity, as many levels as possible are printed in tabular form. In TableForm, the levels printed need not consist of elements with the same list structure. In MatrixForm, they must.