A non-qualified retirement plan for key company employees, such as executives, that provides benefits above and beyond those covered in other retirement plans such as IRA, 401(k) or NQDC plans. There are many different kinds of SERPs available to companies wishing to ensure their key employees are able to maintain their current standards of living in retirement. SERPs are also known as "top hat plans". Unlike NQDC plans, in which key employees defer compensation in order to receive it later, SERPs are entirely funded by the employer. Because of the high costs associated with funding SERPS, they are criticized by shareholder advocates and labor groups that believe some executives are overpaid for their performance.