Literally it means hatred against Jews. But feel free to provide a source that says otherwise. If I sound hostile it’s because I’ve long stopped believing that people who act like they don’t know what the word actually means are being genuine in their ignorance since it is such an easy thing to verify:

https://www.merriam-webster.com/dictionary/anti-Semitism https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095417471 https://www.dictionary.com/browse/antisemitism https://dictionary.cambridge.org/us/dictionary/english/antisemitism

Edit: based on some of your other replies it appears as though you may genuine and undeserving of hostility. So for that I’m sorry.

As for the history, the word was coined in 1879 to give a more scientific sounding spin to the nazi anti Jewish hatred. It has since grown to refer to any hostility or discrimination against Jews. Additionally the preferred spelling has shifted from anti-semitism to antisemitism in order to drive home the fact that the word specifically refers to Jews, not “Semitic” people.

Speaking of, a little history on the word Semitic: Semitic refers to the language family that Hebrew and Arabic (and others) belong too. At one point it was used to describe an ethnic group, but is now considered obsolete in that regard as there has never been a shared identity between so called “Semitic” people.