A type of retirement plan, usually tax exempt, wherein an employer makes contributions toward a pool of funds set aside for an employee's future benefit. The pool of funds is then invested on the employee's behalf, allowing the employee to receive benefits upon retirement. In many ways, a pension plan is a method in which an employee transfers part of his or her current income stream toward retirement income. There are two main types of pension plans: defined-benefit plans and defined-contribution plans.In a defined-benefit plan, the employer guarantees that the employee will receive a definite amount of benefit upon retirement, regardless of the performance of the underlying investment pool.In a defined-contribution plan the employer makes predefined contributions for the employee, but the final amount of benefit received by the employee depends on the investment's performance.