Denial of the Armenian Genocide is saying that the Armenian Genocide did not happen or what happened was not genocide.
From 1915-1923, in the Ottoman Empire and subsequently the Republic of Turkey, the Ottoman/Kemalist government's tried to get rid of some Armenian people in the Empire. The government did this by killing between 800,000 and 1,800,000 Armenian people. They also made many Armenians leave their homes (this is called relocation).
People who deny the Armenian Genocide say that these things partially or never happened. They also say that the Ottoman government never, in an organized way, tried to commit genocide against the Armenian people. For example, the United States of America and Republic of Turkey does not accept that the Ottoman government tried to get rid of all the Armenian people in the Empire.