1891
Eh? Which country do you mean, different countries have different dates. New Zealand for example has Labour Day which was enacted considerably prior to May Day memorials in other countries. But for the US, 1891.
An annual event occurs once a year.
1789
Annual event
Once a year is called an annual event.
Basketball became an official Olympic event in 1936. It was included for the first time at the Berlin Games. Prior to this, the sport had been played in exhibition matches at the Olympics since 1904, but it was not until 1936 that it was formally recognized as a medal event.
Once a year is called an annual event.
Something that happens once a year.
An event of some sort that happens twice a year.
An anniversaryanniversary: the annual celebration of an event on that day of a previous year
An annual event
The Super Bowl is an annual event because it occurs once a year, at the end of each NFL season.