"Antisemitism" is a wrongly used and applied word, so I will try to avoid using it. The word effectively erases other Semites, which include "Arabs": Palestinians, Lebanese, etc.
The correct word is 'Anti-Jewish' which can be followed by 'racism,' 'bigotry,' 'hatred', etc. That would be against "Jews" which is itself a problematic word, as I shall show below, but can be taken determined by identification (people who identify themselves (individually or by collective authority) as "Jews").
Generally, all forms of general racism, bigotry, and hatred are bad things. However, it is more important that people be able to think and speak freely than to avoid all such bad things. Racism, bigotry, and hatred become actionable when they are used in official contexts (such as official statements by a government official), or lead to further crimes imminently, such as racial discrimination or violence.
Often confounded with anti-Jewish racism are anti-Judaism and anti-Zionism. Neither are "races."
Anti-Judaism is criticism of the set of religious traditions known as Judaism. Criticizing a religious tradition is fair game, as most religious traditions themselves criticize other religious traditions. However, once again, civil rights apply to people regardless of religion and so must be avoided in official statements by government officials, discrimination, or violence.
Anti-Zionism is criticism of the geopolitical project known as Zionism, which maintains that (1) the Jews are a people (they are not, see below), (2) that all peoples deserve sovereignty of a particular geographical area (they do not, they deserve to co-exist with other people there), and (3) to achieve those ends, it is acceptable to have an apartheid state, ethnic cleansing, or genocide of others.
"Jews" is not a word used to describe a distinct or unusual ancestry. Historically it was used to describe 'people who follow Judaism' and that is still, really, the best definition, as nothing else fits. That is how I will use the word 'Jews.'
Since its inception (for which the best evidence appears to be around 300 BCE, as that is when the earliest known copies of the Torah are found) Judaism has been and still is a proselytizing religion. Anyone can convert to Judaism so long as they are accepted as such into a Jewish congregation (who have may have differing rules regarding such acceptance, though it typically requires circumcision for males, and renunciation of other "gods" including especially Jesus Christ). Equally important, anyone can covert out of Judaism, as in fact many Jewish descendants have done all along the history of Judaism.
In ancient history, Jews and their predecesssor proto-Jews (such as Hebrews) spread around the world for both voluntary (foreign opportunities) and involuntary (being taken as hostages or slaves) reasons. Voluntary relocations vastly exceeded the involuntary, starting from when Jews took over the international Phoenician trade networks after the defeat and collapse of the Phoenician empire. In other parts of the world, especially in Africa and Eastern Europe, they converted many others into Judaism, especially through marriage, since others needed to convert to Judaism to marry a Jew who wished to remain Jewish. By the beginning of the first millennium of the Common Era, more Jews lived outside of greater Judea than within. (And Greater Judea itself, then known as the Roman Province of Judea, was a vast expansion of the original Judea--a small region surrounding Jerusalem-- through conquests by the Hasmonean Kingdom which were followed by mass conversions to Judaism, making them all Jews by that means, though it may not have stuck for long, as many within both proper Judea and Greater Judea later converted to other religions, especially Christianity and Islam.)
Nowadays Zionist Jews like to feign or impute Greater Judean indigeneity in the claim that they have a unique ancestral connection to that region. But they do not. There were others who were always there, and there were many Jews there who descendants converted to other religions. Meanwhile, Jews have been so widely dispersed into other parts of the western world, and intermarried with non-Jews, sometimes but not always continuing to be Jewish, that virtually everyone in the West now has at least some Judean ancestry too. But the ones who have the greatest Greater Judean ancestry are the people who remained in Greater Judea and simply converted to other religions, including Islam and Christianity.
Meanwhile, the endless attempts of Zionists to label anti-Zionists as "Antisemitic" deserves a word of its own. That could be Anti-anti-Zionism (AAZ). AAZ attempts to erase the civil rights of people to criticize any government, or to denounce the terrible actions of Zionists especially in the middle east. AAZ belongs to the same set of tendencies as fascism. There is also Anti-Anti-Judaism (AAJ), which attempts to erase the civil rights of people to criticize any religion.
