Commonwealth Day, also known as Empire Day, celebrates the commonwealth. Commonwealth Day is observed every year on the second Monday of March. The commonwealth is the vast erstwhile British Empire that stretched from the Atlantic to the Indian Ocean and beyond to the Pacific. Traditionally, Commonwealth Day has been celebrated with a multi-faith service in Westminster Abbey with the queen in attendance. The queen is no longer the monarch of the colonies as there are no colonies but she remains the symbolic head of the commonwealth, just as she remains the symbolic head of British people.
Commonwealth is more symbolic today than anything else. Of course, the countries don’t have any shared wealth or a common treasury but erstwhile colonies that are independent democratic nations today have chosen to stay a part of this symbolic congregation. Commonwealth Day precedes the Commonwealth Games that like Olympics are held every four years and brings together the finest of athletes and sports teams from all member countries of the Commonwealth.
There is a Queen's Baton Relay on every Commonwealth Day held at Buckingham Palace. This is also similar to the torch that travels the world leading to the Olympics. The baton handed over by the queen to the first relay runner then travels the commonwealth nations, finishing the relay at the opening ceremony in the country that hosts the Commonwealth Games for that edition. Commonwealth Day is not a holiday in any member nation. It is not even well known in countries that were colonies of the British Empire. Commonwealth Day is more of an old ritual, mostly symbolic and it does have some historic relevance, but no member nation performs any special program or feels in any way connected to the kingdom. The public in Britain and in erstwhile colonies are largely unaware and uninterested in the commemoration.