The keyword phrase "patriots day bombing date" functions primarily as a noun phrase. Specifically, "Patriots Day" is a proper noun acting as an adjective modifying "bombing," which itself is a gerund acting as an adjective describing "date." "Date" is the core noun of the phrase. Collectively, the entire phrase refers to a specific calendar day marked by a significant event.
The "Patriots Day bombing date" refers to April 15, 2013. This date marks the occurrence of the Boston Marathon bombing, a domestic terrorist attack that took place during the annual Boston Marathon race. The marathon is traditionally held on Patriots' Day, a civic holiday celebrated in Massachusetts and Maine, commemorating the battles of Lexington and Concord, which initiated the American Revolutionary War.
On this date, two pressure cooker bombs were detonated near the finish line of the marathon on Boylston Street, Boston, Massachusetts. The explosions resulted in the deaths of three spectators and caused severe injuries to hundreds of others, including many who sustained traumatic amputations. The event triggered a large-scale emergency response, a multi-day manhunt for the perpetrators, and a profound national impact, becoming a significant moment in the history of domestic terrorism in the United States.