Dividends in arrears refer to the accumulation of the dividends that the preference share class has. The preference shares accumulate dividends even when no dividends are declared. In this case, the accumulation will be disclosed in the notes. If the dividends are declared, the accumulation of these unpaid dividends is recognized as a current liability.
In addition, if a company declares dividends but not paid yet (even for ordinary dividends), it will need to create a current liability (dividends payable).