Real world article
(written from a production point of view)
According to background material created for the Picard family album but not ultimatly seen on-screen, the Committee for Quadcentenial was a committee created by the Daystrom Institute for celebrating the 400th anniversary of the Apollo 11 moon landing. Centennial was incorrectly spelled with one n.
In a letter sent by this committee, Jean-Luc Picard received confirmation that he would be attending the "commemoration activities for the lunar landing activites." The activities, consisting of receptions and parties, would commence on July 16th and end on the 20th.
The quadricentennial is known to have occurred in canon, as Harry Kim is shown to have attended it in the Star Trek: Voyager episode "Nightingale".