The Holocaust refers to the mass genocide of Jewish people, who were targeted simply because they were Jewish, regardless of age etc. They were subjected to ever growing restrictions, laws, placement in ghettos and eventually the Final Solution. There are multiple sources, on the web and in books which support this definition.
The deaths of others, which were no less horrendous, were due to wider Nazi ideologies, often based around their specific ideals of family and the importance they placed on creating a strong Germanic race.
The classification of prisoners in concentration camps gives a good idea of how they viewed different groups of people, where each group was given a different coloured star depending on the type of prisoner they were, e.g. yellow for Jews, red for political, pink for homosexuals. Jewish and Roma prisoners were specifically marked out for systematic murder, whereas the other groups of prisoners were not (although many did die in camps through malnutrition and disease).
I find it disgusting that people with specific ideologies and agendas but no knowledge of the history of this era, past what they have googled (and judging by most of my students, not got past Wikipedia) are trying to rewrite definitions and history. I'm a History teacher and have specialised in this area - it worries me what some of my students will be reading when we study the Holocaust later in the year. Thank you for this thread, it's been incredibly enlightening about what is going on, and the debate surrounding it. There have been some great links posted that I will use too.