Posterity - all future generations of people. (Don't worry, the definition is for me to make sure I am using posterity in the right context.)
I was delighted when I found five letters my great grandmother had written to my grandparents. It was a time capsule of 1918 and 1919. It had clues about the family but it also shared daily bits. She wrote how they had managed their timber so they would get better prices. She talked about the people who ran the mine. She talked about the "flue" and how many people were sick. You can read about mines and the flu in history books but the emotions and day to day details are absent.
Writers and bloggers are leaving information for posterity. Never in our history has there been so much available. Genealogist may complain that the data is not verified but that's not as important for family historians. I know I am after the flavor of the times as well as the details.
Based on the letters, I know that my great grandmother was educated in an area where girls did not learn to read and write. I know that she bought property and had an income greater than what the farm provided. I know she treasured her children above all else and had a hard time letting them go, even as adults. I know she was strong and able to survive tragedy.
My family tree is full of wonderfully unique people who left clues for their descendants. They didn't leave large estates or millions but something greater. They left a family history full of life events telling us who they were, what their dreams were, and how they achieved their goals.
Just like the letters written by my great grandmother, today's writers and bloggers are leaving little bits and pieces to posterity. How great is that!