Explain what is anti-semitism?

Antisemitism, also known as Judeophobia is a term used to describe prejudice against or hostility towards Jews, rooted in an aversion to their religious/cultural/ethnic background

The term anti-Semitic or anti-Semite usually refers to Jews only. It was coined in 1879 by German journalist Wilhelm Marr in a pamphlet called, The Victory of Germandom over Jewry. Using ideas of race and nationalism, Marr argued that Jews had become the first major power in the West. He accused them of being liberals, a people without roots who had Judaized Germans beyond salvation. In 1879 Marr founded the League for Anti-Semitism.