The word supercede means to take the place of something or someone else. It also can mean that something may be force out or set aside and another person or thing has been put in its place because of its higher favor.
There are many examples in finance where you will have documents that will supercede others. For example, if you are married and accrue debt together with your spouse using credit cards or other types of debt, you are both responsible for the debt. This sounds like a no-brainer but if you and your spouse decide to divorce and a collection agency comes after you about a debt that your divorce decree says that your spouse will pay; it is actually the debt that supercedes the divorce decree. If the decree has been violated (i.e. your spouse not paying a debt that the decree stated was to be paid by him or her) then you can use that decree to take your spouse back to court and fight the battle over who pays the debt there. But, your divorce decree does NOT supercede your debt that was jointly accrued.
When settling end of life affairs, many people wonder which documents might supercede others in the event of death. For example, if you have a will that decrees how your assets are to be divided and you also have life insurance policy that may conflict with some of the information on the will; it is the life insurance policy that will supercede the will. The documents do very different things.