A defined benefit plan is a pension plan where the future payout in retirement is defined by a set formula when you join the company. It is a calculation that usually includes your highest average salary, time working in the company, and how much money was contributed by you and the employer.
The money is invested on your behalf and the firm is responsible for risk if something goes wrong. There is usually an implied rate of return that is guaranteed by your employer each year, which is the investment rate of return your money would earn if you could see your pension plan in a bank account. You can also get the information about international pension planning through various online sources.
A defined contribution plan is where the money you pay into the plan is defined: the amount contributed either by you or on your behalf by the company. It is a set dollar amount based on your salary in the year that you are working. You can think of it as the company (and sometimes you and the company) contributing to your pension account.
A defined benefit pension plan is basically a giant bank account, covering retirement for many employees in an organization over a long period of time. The employees and the employer contribute money every year, and this money is collected in this account.
The entity that manages this bank account is called the plan sponsor. This account is typically run separately from the company operations, or from the institution it represents. For example, the GM pension plan is a separate entity from GM the corporation.
The only relationship the pension plan and the underlying company should have is for company contributions, adding money to increase funding of the plan, or removing money over and above the projected amount needed to pay the present and future pensioners.
If there is any other money transfer between the pension plan and the company, this should be monitored as it may signal funding problems, or a permanent change in the structure of the pension plan (for example company mergers, amalgamations or division split off from the parent company).