Examples of this include:  controlling shareholders might extract value from a firm at the expense of non controlling shareholders;  managers may award themselves huge salaries or bonuses unjustified by their actual contribution to the success of the business, and;  managers of a firm might evade paying its proper tax liabilities.
These actions are damaging not just because they transfer resources from outsiders to insiders of a firm, but also they create incentives for actions which are socially sub-optimal.