Long replay from Marg's Man.
Hexemaus asked this question last year which I answered in a PM.
ANZAC Day is 25 April and very important to most Australians. Here's what else I said...
Actually Marg misspelled it when she wrote Anzac because the word is actually an acronym A.N.Z.A.C.
The letters stand for Australian New Zealand Army Corps
ANZAC Day - 25 April - is probably Australia's most important national occasion. It marks the anniversary of the first major military action fought by Australian and New Zealand forces during the First World War on 25 April 1915. The soldiers in those forces quickly became known as ANZACs, and the pride they soon took in that name endures to this day.
If you follow this link to the Australian War Memorial page on ANZAC you get a great deal of information
http://www.awm.gov.au/commemoration/anzac/anzac_tradition.htm
More information on Gallipoli itself can be found at
http://www.anzacsite.gov.au/1landing/index.html
ANZAC Day is special to me because my father and both his brothers served overseas during World War II. All three were in England during the Blitz then went on to Africa to fight Rommel. A maternal uncle was one of Rommel's "Rats of Tobruk". The older brother was wounded and sent home to recover. Dad and his younger brother then went to Greece where their units pushed further into the Italian held lands than any other Allied Units. Such was the secrecy of the War that neither knew until later that they had been in the same battles. They met on Crete in late 1941 when one of them heard that there was an Australian unit nearby and went to investigate. Neither knew the other was in the region. Dad was captured by the Germans when Crete fell, escaped soon after and spent over a year in the mountains of western Crete with the Greek resistance. We have many friends in Greece to this day. Captured again, he was questioned by the Gestapo and spent the rest of the war as a POW in Silesia and eastern Germany. The youngest brother got off Crete when it fell and was sent back to Australia. He was then sent to New Guinea against the Japanese crossing over the infamous Kakoda Track in the New Guinea highlands.I only discovered this year that his unit is the only Australian unit that can claim to have fought all the King's enemies having fought the Germans and Italians in Europe and Africa and the Japanese in the Pacific. This year is the 60th anniversary of those battles in which a small force of ANZACs opposed a numerically superior Japanese force. The most famous of those battles is commemorated in a carefully researched new film "Kokoda" released on 20 April 2006 that celebrates the efforts of the 39th Battalion an understrength militia unit that held off the Japanese for six months. The film's website is
http://www.kokodathemovie.com.au/
I am, technically an ANZAC myself, having served in the Australian Army Reserve for 5 years during the 1970's but I don't really claim the title. I feel it belongs more correctly to men like my father and my uncles. As part of the Vietnam generation this was an unpopular move with my peers. While I felt that we should not have been in Vietnam; I saw the need for there to be a military force and took the steps I did to stay out of Vietnam but to be ready in case there was real need for conflict.
Australians are peaceable people in general with a strong sense of loyalty (mateship) who can be the best of friends or the worst of enemies, sometimes both. The Turks have found this out and the ties between the two countries are so strong that the 2006 ceremony at ANZAC Cove in Gallipoli was actually conducted in English and Turkish with Turkish soldiers taking an active part in the commemoration.
I written a lot but your very simple question has a very complex answer and I've still barely scratched the surface. From the Americans I know here, the nearest you have to it is Veteran's Day but only if you cross that with the nationalism of 4th of July. It is a day to honour our fallen, to celebrate the survival of those who came back and to reflect on the necessity, and futility, of war.