Linguistically, "antisemitism" refers to prejudice against the semites: which include a collection of semites ethnicities that have historically lived on the Arab peninsula including the Jews, Palestinians, and other Arabs.
However, for most of modern history the term is generally used specifically describe a hatred or prejudice against the Jewish people. Yet recently, the term is beginning to loose this popular meaning too.
Specifically, the term now may as it is now being used around lightly to describe anyone who criticizes the state of Israel especially with regards to its war crimes against the Palestine people. This issue is primarily exasperated by high ranking Israeli officials in Israel's right-wing government who have a tendency label any individual or entity that have express support for Palestinian self-determination or upheld the internationally recognized right to defend itself from illegal occupation as "antisemitic".
Critics warn the rampant misuse of the label "antisemitism" is already making the term loose is linguistic effectiveness for when describing "true" cases of "antisemitism", comparing the shift to the popular fable of "the Boy who cried wolf".
Old usage example:
"Hilter is the epitome for what antisemitism looks like. He slaughtered millions of Jews for simply being born. Hitler was a criminal."
New usage:
"40% of the casualties in the Gaza-Israel war were children. Israel has no regard for the lives of children, let alone regular civilians and aid workers."
"That's the biggest boat load of antisemitism I've ever heard in my life."