“abusive or threatening speech or writing that expresses prejudice against a particular group, especially on the basis of race, religion, or sexual orientation” Google dictionary .
Here is examples of hate speeches .Here is why a hate speech is not an free speech. A hate speech is basically abusive writing to a particular group of people .
Images from .
https://blog.twitter.com/en_us/topics/company/2019/hatefulconductupdate.html