A more thorough explanation:

Definition: Posterity refers to all the future generations of people. It can also refer to all the descendants of a person, including those who are born many years later.

• It is important to protect the environment for the sake of posterity.
• The founding fathers of the United States created a constitution that would benefit posterity.
• My great-great-grandchildren are part of my posterity.

The first example shows how we should think about the future and the impact our actions will have on the generations to come. The second example illustrates how the concept of posterity was important to the people who created the US government. The third example shows how posterity can refer to our own descendants, even those who we will never meet.