El Dia de la Hispanitat in Catalan refers to the National Day of Spain on October 12th, which is a public holiday throughout Spain but is only celebrated by a minority of people in Catalonia.
The Day is also known as Columbus Day in the United States because it was on October 12th that Christopher Columbus arrived at San Salvador, now known as Watling, in the Bahamas and officially "discovered" the Americas.
For the same reason, the day is known as El Dia de la Raza or The Day of the Race in much of Latin America because it was when the European and indigenous American peoples and a new race was born as a result of their mixing.
There is a large minority of patriotic Spaniards in Catalonia and quite a significant Latin American immigrant population who celebrate the day but it is treated as little more than a day off work by most Catalans, particularly as the independence movement has gathered pace since 2012.
In Madrid, there is a military parade attended by the royal family and most politicians and if you switch Spanish television, there are people marching often with goats and lots of tanks driving by.
In Barcelona, there is usually an anti-independence demonstration in Plaça de Catalunya attended by a few thousand people, members of political parties, like Partido Popular and Ciudadanos, and unionist civil society groups, such as Societat Civil Catalana, whilst a smaller demonstration in Plaça d'Espanya tends to attract more radical right-wing groups.
October 12th is also the Saints' Day of La Mare de Déu del Pilar, who is the patron saint of Zaragoza.