The subject of the query, "Patriot Day," is a proper noun designating an annual observance in the United States. This day is observed on a fixed date each year: September 11th. The date is static and does not change annually, as it was established to directly commemorate the victims of the terrorist attacks that occurred on September 11, 2001.
Established by a presidential proclamation following the attacks and later designated by law as the "National Day of Service and Remembrance," the observance is a day of solemn reflection. It is important to distinguish this day from "Patriots' Day," a regional holiday in some New England states that commemorates Revolutionary War battles and falls on the third Monday in April. On Patriot Day, U.S. flags are flown at half-staff, and the nation is called to observe moments of silence corresponding to the times of the 2001 attacks.
In conclusion, the date of September 11th is the defining characteristic of this observance. Its fixed nature is integral to its purpose as a memorial for the individuals who lost their lives and a day for national unity and remembrance. Unlike holidays tied to a day of the week, its specific date connects the observance directly to the historical event it honors.
